Update: mudding finally done in the spare room

That thinned-out final coat trick saved me on my basement reno last fall. I was using Plus 3 out of the bucket for everythign and wondering why I kept tearing the paper with my 12 inch knife on the taping coat. A buddy who does this for a living told me to add water untill it spreads like cake frosting, and suddenly the whole job felt diferent. For the finish coat I probably thinned it almost to pancake batter and it basically sanded itself. The part where you said you kept messing with spots that were allready close, that hit home. I did the same thing on my first room and every one of those patches came back to haunt me. Now I force myself to walk away and check it from across the room instead of up close, because your eye at six inches sees stuff the wall will never show. On the primer dread, I acutally came to like it. Hit the walls with a work light raking across them at an angle before you prime and you'll catch most of the low spots and pinholes ahead of time. Primer will still find a few, but a quick skim and a second pass with the roller and mine came out clean enough that nobody can tell I'm not a pro.

Before you prime, do yourself a favor and check the walls with a bright light held right up against the surface, raking it sideways across everything. I learned this the hard way on my garage conversion. I thought my flat coat looked fine under the ceiling fixture, taped up the plastic, rolled the primer, and suddenly every seam and swirl mark lit up like a topographic map. Had to wash the dust off, spot-fix a dozen places, wait a day, and reprime half the room. A cheap LED work light works fine for this, just hold it low and angle it across the wall instead of pointing it at the wall. The shadows tell you everything. I also keep a damp sanding sponge on hand for the touch-up pass instead of dragging the pole sander back out. For small stuff it leaves a softer edge than dry sanding and there is basically no dust, which matters when the room is already taped off. One thing I stopped doing years back is sanding between the tape coats. I used to knock down every little bump after coat one, but now I just let the second and third coats do the leveling. The only place I sand early is where the tape edges peek through, and even then just a light kiss with the sponge so the next coat covers it.

The raking light thing is so true. I clipped a cheap LED shop light to a step ladder and moved it around the room between every two coats, and it caught a crowned seam over the doorway that I never would have seen from standing flat in front of the wall. Fixed it with a light skim instead of finding out after primer like I did in my last place. Also second the walking away habit, mine got way better once I started leaving the room entirely and coming back ten minutes later with fresh eyes.

I really connected with what you said about getting stuck trying to fix spots once they're close. It felt like the mud was just getting thicker and harder to work with the more I kept trying to patch it immediately. I'm having trouble figuring out how long to wait for each layer to get solid before I move on to the next section. It seems like timing is everything to avoid those hard bumps later.

I'd push back a little on the pancake batter thing. Thinning helps on the finish coat, sure, but if you go that watery the mud gets weak and shrinks more, and I ended up with sunken patches that showed up after the paint went on. Half a cup of water per scoop is plenty to knock the stiffness out. And one thing I do differently now is skip the pole sander on the final passes, a sanding sponge in my hand gives me way more feel for when a spot is actually done instead of grinding past flush.