Itll look good enough to flip if that's what you want. the smoothness and finish is easy to achieve it's just a bit of work. If you want it really flat and smooth no problem ! Just do a couple more passes to work out the imperfections. if it's not perfect enough do more. If you are good at applying mud you'll achieve "perfection" in lass coats. if you suck at it itll take a couple more coats and in the meantime you'll get better at it. the sheen relates to the finish of paint you put on and how you apply it, it not whats underneath the layers. If you have bulges you'll have to build out the finishing coats more than whatever lump sticks out he most. That's just the same as when you do drywall and you have a screw head sticking out. if the bulges stick out lots then itll take lots of mud over the rest of the wall to make it flat. The weight of that mud will be added to the keys but when dry the mud isn't that heavy. . If you don't reinforce then you can do a lot of work making it perfect but you may be really only hiding the attachment issues. It's not going to just fall away all of a sudden but if the plaster isn't stable and you make it look perfect then you may be disappointed to see problems return when the cracks work their way through or if the keys give out then you may see chunks coming away like you have in the picture. drywall tape will help somewhat to stop fine cracks from continuing through the mud. You can't stabilize the wall with paper tape on the surface. If you want to do a coverup, make it smooth , sell it, you can.
If you hit plaster hard it cracks. if you hit it again it spiderwebs more. hit it more times and itll get to the point where they keys fail and after so many hits it'll reach a point where each hit will take a square foot off and itll crash to the floor. Some of that cracking is under the paint but you can't see it . you can only see where the plaster has given way and coming away from the lath. You can tackle that by removing it or trying to reattach just a localized area. or by laminating more drywall to the wall. If you want to remove the plaster completely just hit hte wall multiple times and within a minute you'll be seeing the plaster on the floor. in a half hour you can remove all the plaster in the room just by hitting the walls with a hammer. then you can pull the lath off if you want to. then you can insulate and rebuild the wall .it's messy. you'll have to cart the mess to the dump.
if you want to repair that 2 square foot chunk that's bothering you you can try this :
first turn off the breaker for that room just in case you are unlucky enough to cut a wire in the wall.
1- cut the lath and plaster to the studs on either side and do a drywall repair or a plaster repair. if you want to remove just a section you can cut it flush with the studs on either side with a jigsaw and a fine blade. cut slow so it doesn't shake the wall too much. follow the stud you'll feel it with the blade once you get going or you can make a cut and stick a piece of bent wire. through the cut and feel for the studs. the lath is nailed to each stud it crosses so don't cut that. It'll shake less if you cut right beside the stud as that's where the lath is secured.
2- Sister the studs with a couple new 2x4 so you have something to screw your patch to.
When you cut the drywall you can cut it 8 inches larger in both dimensions and then cut the backing paper size to loosely fit the hole. ( 1/4" smaller than the hole) Snap the drywall plug and peel the face paper off the 4 inch scraps leaving a drywall plug with a 4" face paper flange. inspect the flange and remove any drywall bits stuck to the back of the face paper flange. . You now have a plug for your hole and means of screwing it on.
3 - butter the back of this flange and around the edges with LOTS of taping mud. any excess will ooze out. that helps key it in. . Screw your 2 foot square patch to your new studs. Use your taping knife to smooth the face paper flush with the surrounding plaster. it'll come out perfectly flush and you'll hardly see the repair even before you start skim coating.
tip: when you sister your new studs position them so that your drywall fits flat or just a hair lower than the surrounding plaster. You can probably use 5/8ths or whatever you have around. If you wanted to use lath and plaster instead of drywall you can but it will take longer and look the same when finished.
personally I find it hard to do coverup type work, but if you are asking if you can make it flat and smooth and perfect looking just by applying mud, yes you can.
one thing you should know is that older drywall mud. like stuff from the 50's tot he 80's may have asbestos in the mud they used. If your plaster walls have been repaired with drywall mud during the era that they added asbestos to drywall mud than you should be careful about breathing it. this is mostly a concern for those who are removing drywall from that era but it was also often used to repair plaster walls so you might not be in the clear just because it's a plaster wall. if you want to know for sure you can take the samples for testing. I took some from my living room and it's about 50 bucks per test. you'll need to give them a small sample of the mud to check.