You would only need to sand if the surface is rough. Usually if you use a good primer, the paper facing of the drywall does not raise that much to cause the surface to be rough. All it takes is a quick pole sanding...you hardly have to apply any pressure. People get all freaked out by hearing they have to sand...it's not a big deal, seriously. Get yourself a pole sander. You can buy them with the sanding pad attached already, or you can just buy the sanding head that screws onto any standard extension pole. Put some 150 grit on there and you are good to go. The first couple walls with the pole sander will be a bit tough going, but once you get that sheet of sandpaper broken in, you should be able to fly. Granted, some people have no coordination and can't pole sand....but just don't try to press too hard. Check your work with your hand as you go to get an idea how much pressure you need to apply. It shouldn't take much to get those walls perfectly smooth. You should only dust if there is dust on the walls. Gravity usually takes care of the dust. It's minimal anyway when you are just sanding primer that is not that rough. The only time dust becomes a real issue is when you are sanding patching. The reason we may dust is because we want the topcoat to adhere to the primer. If you paint over a pile of dust, obviously that dust may impede that topcoat from sticking so later it will peel. You probably do not need to sand after the first coat. Generally, there is nothing that will make those walls rough again after your initial sanding unless you are painting with old paint that is all snotty or you are using a cheap roller cover that sheds all over. Then you would need to sand off the roller lint and snots. If your paint starts to get snotty, strain it. You can by strainers at the paint store or use some old nylons.

Its a regional issue but when you want something different it often becomes a matter of skill. Where a higher level of skill is required the subs simply learn how to do it. In the Boston area there is a 400 year old tradition of smooth plaster that can be painted or wallpapered. Today taped drywall is generally a DIY method; professionals use a skim coat finish called "veneer plaster" on an absorbent drywall base called "blueboard". For decades it has been cheaper than taped drywall because it is so much faster to finish (no sanding). Now its about the same cost and if you don't tell the contractor you want taped drywall you will get veneer plaster. The veneer is only 1/16" thick but its very hard. The finish is flawless and fewer coats of paint are needed and they last longer. Unfortunately, you only have to drive 50 miles south west of Boston to find builders who have never heard of it. Nevertheless, its well worth the effort to search for blueboard installers in you area.

James- hi! I did a remodel and the original builder (since fired )paid no attention to the fact that we wanted to paint the windows black with mullions even though we spent a fortune on rounded sheetrock returns and he knew it. Our windows were ordered with the jamb too short (and not thin enough to be pretty painted black- like an in between 3” jamb on a 5” wall) so a jamb extension was done by the trim carpenter that didn’t quite line up well and now I have NO idea what to do. It is such a mess! Also, didn’t you find it hard… I want to do white dove wall with simply white base molding, but I’m not sure if I need to then paint the wood that joins the windows white dove or simply white.. with the mullions black! It’s almost like I might be forced to do a white dove base molding. How did you handle that??

Requirements for egress differ from place to place. Where I live (Ontario Canada) it's enough to have an egress window somewhere in the basement, in addition to the main staircase exit. The window doesn't need to be in the bedroom. It may be different where you live, or you may want to put in a bedroom egress window even if your code doesn't require it. So be sure you budget for that expense if you don't already have what is required. The requirements for a legal bedroom, size-wise, also differ from place to place. If you want to list it as a bedroom when you sell, be sure you build it to the adequate size for your location.