yes you can skimcoat over paint if you want to but i'd rough up the paint first and if it is falling apart then it won't help. you could use a random orbital sander on the existing paint with about 80 grit to roughen and flatten the wall. if it's leaded paint then dust may be an issue.
its possible to V groove your plaster cracks and fill them. It is also possible to use my glue and tape method to stop the cracks from coming through. you cna use washers but if the key is broken the plaster may not be very stable. If you start hammering on a plaster wall it will crack, then crack more then it will all crash to the floor. it is very brittle stuff. as long as it isn't super cracked up it is fixable.
yes you can fix the plaster if you want, repair the cracks and skim coat and repaint.
how much do you care about having the original plaster?
its already insulated so you don't need to open walls for that.
I'd pull the baseboards and trim, you can strip the paint and show the wood if you want .
use 1/4" drywall its not too heavy so it will make lifting easier and you don't' have to demo the walls.
if you put 1/4" drywall over the side with the windows you'll need to cut strips to fill the space between the window frames and window casings. You might choose to restore the plaster on that wall to keep the original thickness.
the skimcoating you can learn and if you have questions just ask. You have a chance to practice if you are up for it. It will definitely get you moving around and I can't judge if you are up for it but it isn't heavy work really, just lots or reaching and it will take time. You can always get a drywall filler to help if you get sick of it. you can rent or borrow a drywall lifter to do the ceiling. the stuff on the walls wont' be too hard. If you want just nail a board to the wall about 1/4" lower than the bottom edge and you can set the drywall on that and then pry it up to the ceiling and get your first screws in so you aren't trying to hold the sheet and screw it on. If you have a helper all the better.
if you don't' want to rent the lifter just screw a couple 2x4's together to make a T make it about an inch short of the ceiling that way if you are able to lift it up then you can stick your T in underneath to hold it up there while you go look for your screw gun you can make 2 or three T's. Once you get a few screws in you are home free.
if you lean one T against the wall then you can lift one edge on top near the ceiling and then stick the other T in and I sometimes just do it myself this way With a back issue you need to be more careful but you can still likely manage the 1/4 inch stuff if you use that.
You have to locate all the studs. don't try to screw to the lath it won't grab. You can drill with a tiny drill bit and note where it will poke through into the insulation , if you get the bit in an inch you know you are through the plaster then if the bit can be pushed easily you didn't hit the stud.. once you get going you can find them all and mark them and then snap lines. that way all your screws can hit the center of each stud. be careful not to drill into any wiring.
Its hard to judge the condition of the actual plaster without stripping. the cracks can telegraph through your finish if you don't fix them and just skim coat. If you feel it's destructive to put 1/4" drywall in front of the plaster than don't do it but i think that's the fastest and easiest way to achieve a perfectly flat wall If that's what you want.
If you chose you could repair the cracks, strip any loose paint and then primer, skim coat, primer again , then paint it.
one thing that might mess you up is if you have layers that aren't attached well now. If you just skim coat you can make it look perfect but it might not last if it isn't at least a stable surface. in many houses the initial paint coat n top of the plaster was water soluble calcimine paint so you could have issues with that failing and you could likely just strip a little spot to see whats under there and if it's water soluble. If its not stuck good, well it's disappointing if you finish it and then have adhesion issues but likely you'd get away with it.
all the reaching may hurt your back or it might be just perfect exercise for your condition. I don't know but other than that you can do it, you can learn any technique and you could watch a few Utube videos on skim coating and taping etc. I just watch lots and then do it my own way but it's a good way to get some good tips.
I'm doing my living room now. If I wanted it fast I'd hire it out but I am happy to take my time and I do a lot of things a commercial guy just wouldn't take time to do. for example I use corner bead in every corner instead of tape. i mix carpenters glue in the mud I use for taping and initially. I soak the tape and the ( paper-metal) corner bead in a 50/50 glue/water mix. I don't' use mud with glue that to fill at all , this gets the tape and corner bead super flat with the wall , then I start skim coating.. the commercial guys put more mud behind the tape, then they use filler to build out the wall near the tape and hide the tape that way. My way takes longer but I get a better job that way and my tape never ever lifts or peels..
if you mix carpenters glue into your mud it makes it as hard as plaster. it cheap but you can't sand it so it's something you have to be careful with. you have to catch any drips or runs or they cause trouble. It isn't for surface filling I do use it to fill gaps and attach my tape but I never try to build the surface using my glue mud mix.
if you have huge gaps to fill you can mix some plaster and add that to mud. it dries fast so you only have limited working time but if you have say a 1/2 x 1/2" gap in your drywall you can fill that in one go before you begin taping. If you did that with mud you'd have a drippy mess and if it did stay in the gap it would shrink and crack and you'ld have to do it a couple times.
I fill the gaps before I tape or mud. I do lots of skim coating to get a pretty perfect job. I don't' use paints or brushes to create a lot of stipple to hide my defects I instead work a little harder to get them more perfect and smooth without waviness. It all takes time.
if you hired a "real drywaller" to do it they would use tape on all the inside corners, not corner bead. the corner bead makes the corners straight and crisp. they usually just use the corner bead on outside corners so if you knock the corner it doesn't damage so easy. They wouldn't spend a lot of time filling it before applying tape. they have machines to apply the tape and mud very quickly and they are pros at it . they can do it a lot faster than you or I can but you have to pay them
if you went the 1/4" drywall route you have some trim off the baseboards and the room would become 1/4" smaller the outlets would no longer be flush so you can move them or you can use "box extenders" I just moved mine and made them right. I wouldn't bury the baseboards or they will be thin and it'll look like a crappy reno. I run my drywall to the floor and then put the baseboards back over top later. if you pull your baseboards you may be able to see better how the insulation is in there. they might have sort of glued the baseboard in place if they used foam. the lath probably stops just above the baseboard. you might have a chance to stuff more insulation in there from below. you'd have to open it to see whats going on there.
I used 1/2 inch on some walls. I put 1/2" on the ceiling because you want it really flat. the 1/4" stuff does flatten the wall but if the wall is warped it will follow the warp as it is more bendy than thicker stuff. what I do is use green glue
http://www.greengluecompany.com/You can glue the drywall on , the green glue isn't glue for attachment, its is only for soundproofing. you still screw it on with as many screws as normal. Its possible to glue the drywall on with something like PL glue and just use a few screws but I don't' like that route. the screws pull everything up tight.
never use drywall nails. the only place I use them is to put just a few near my corner beads. I don't' nail through the bead I just put them right beside the tin so the head of the nail holds the tin part. I just use a few so the corner bead can't pop before it dries but it really isn't' necessary. there are a variety of types of corner bead. I like the onethat is metal with a thin paper on them. I found heavy ones and light ones. I use the lighter ones for inside corners, they dont' get knocked. i use the heavy ones for outside corners.
In my case it is very noisy so I opened walls and insulated and used sound proof drywall
https://www.quietrock.com/If you do any walls that may end up being a shared wall with a suite use 5/8ths fireproof drywall to meet code or check your code.
Phil
