A month on, another side painted, in stolen moments and hours. For "side 2", which was faster than side 1 because I didn't have quite so many first-time mistakes to make, I thought I'd give an overview of the steps in case it helps others in the future.
I started with a light sand, 240 grit, over the spray surface that I already had. Just a quick sand before I got going with the roller for a first coat. Don't worry like I did about the state of this first coat. Lines are fine, bubbles are annoying but unavoidable unless you lay off with a brush. You're going to be sanding all the surface away anyway. I'd PROBABLY lay off with a brush to get rid of the hassles that bubbles create (pits, that you'll spend an eternity trying to fill and still end up with a billion of them) but the paint dries too fast for me to do this effectively. Don't bother trying to roller over your finished coat trying to get a better finish with less lines. This just seems to result in more bubbles, presumably because the ones made when the paint is wettest have the greatest chance of collapsing. Re-rollering paint that's dried even slightly (like ten minutes later) gives more bubbles. I tested this "scientifically" by doing a second roll on one half of the cabinet. It looked better until it dried, after which it had loads more bubbles than the side I left alone. You can just about make this out in this picture - top-right diagonal area didn't have the extra roller attention.
After this coat I went over with 240 grit, always wet sand, but this is mainly just about taking the top off any bubbles, so don't spent too long. Then another coat of paint, after which it looks like this.
This the the bubble-ridden glossy coat that you're then going to destroy again. After a bunch of sanding with 240 it looks like the below. I tend to work down the cabinet with a sanding block in lines, using circular motion in areas no more than twice the height of the block and just slowly working down the cabinet, then returning to the top for another vertical pass until I've been over the whole cabinet. This just helps me keep track of where I've covered and to make sure all the cabinet is getting the same attention.
At this point the cabinet has had its initial spray coats and then two coats with a roller. Without the roller coats I'd have needed at least an extra coat I reckon to get to this point. You can see there are still loads of low points in the paint from roller texture and bubbles, but the matt/flat areas are starting to get there.
The trouble with wet sanding is that it's usually hard to see what you're working with when wet. As you can see here, when wet it already looks pretty good, but in the dry areas you can see it still need a load of work.
After a decent about of work with the 240 it lookes like this. You can see it's now flat in more places, with the remaining low spots still shiny and obvious.
It's really tempting to drop to a higher grit, and I've made this mistake loads of times, but you have to get the surface right before moving on. Otherwise you'll spend an eternity and not achieve anything. Also, don't forget to change sandpaper. This sounds like the most obvious thing. But you can spend hours breaking your back and arms sanding, and seeing the paint come off and make the water red so you feel you're making a decent impression, only to then change the sandpaper for a fresh sheet and see what a massive difference it makes straight away. This would all be faster with an even lower grit, but then you have more scratches to deal with. It's a balancing act.
At this point I hit a problem. I'd planned to put two or three extra coats on, slightly thinned to help the paint reach those dips, but I was running out of paint fast and everywhere had sold out of the stuff. I made a decision to continue in a less than optimal way, just in case the paint never came back into stock. In order to conserve paint I opted to focus my extra paint on the areas that demonstrably needed an extra coat - all the areas where the coverage wasn't even or where there were large clusters of bubble remnants. This is risky. It means that I'm more at risk of sanding right through the paint where it's not thick enough, plus it means more work sanding away "patches" and still getting the overall surface even. I wouldn't have done this if I could have got hold of more paint.
After sanding this lot back I then repeated this technique a second time.
The good news is that I was able to get the surface even still. After a load more sanding, still at 240, it looks like this. Note the left edge still has a bit of work needed.
But it's looking quite nice when wet now.
Unfortunately, my fears were realised and there was a spot of white coming through on one edge, typically in a very visible spot.
I touched this up with a drop of paint. This kind of touch-up is tedious because you pretty much have to wait a day for the paint to dry.
Unfortunately it didn't work either. Once I'd sanded away the "blob" that I'd created I ended up with the white coming back through again, so I had to roller on an area about a foot wide to allow me room to blend down the raised surface, then a second roller coat about half a foot on top of that to give the edge two coats. I saw "two coats" but I was literally working with what I had left on the roller at this point. Paint tin was completely empty and I was having to keep the roller wet overnight by wrapping in plastic. Luckily I just about got away with the repair. There's one new white dot that's appeared about an inch from the edge, but I think that might actually be something that got in the paint that I've now exposed in sanding rather than the actual wood/undercoat surface.
After this it's a case of lots more sanding working up through the grits. I used 320, 400, 600, 800, 1000 (maybe...), 1200, 1500 and finally 2000 on this. For the lower grits I was maybe going over the cabinet once or twice, with only once over once I reached the higher grits, except where I could see scratches etc. that needed a bit more work. In close-up the corner looks like this after all that sanding. This is better than the other side looked, or at least it's more even over the whole surface.
I picked up some Meguiar's Ultimate Compound this time to see if it does anything to help with those really fine surface scratches. This is the same corner after applying it. There are still plenty of scratches to be seen, so I'm not sure how much difference it's making. It's taking plenty of red off onto the applicator sponges, so it's doing SOMETHING.
It doesn't wipe off well though and I feel like it started to make the paint perhaps a bit softer or sticky, but not so much as when I tried with t-cut. I certainly found that even a microfibre cloth wiping over it would leave a slight mark on the surface.
After Swirl Remover it looks like this:
Nice and shiny, but you can really see that edge scratching and you can see all the tiny bubble dots. This is as good as it's getting though!
So I'm undecided on the Ultimate Compound, but gave the whole cabinet a going-over anyway.
You can see here the striping from just wiping it off with a clean applicator sponge. I decided this was better than what I was getting when trying to rub it off with any kind of circular motion, leaving the Swirl Remover to sort out the final surface. This shot is with the Swirl Remover well underway, but you can see the duller areas on the left where it still needs to be properly finished.
And, finally, partially unwrapped and back on its feet.
Celebration, unfortunately, was short-lived, because lifting it back up uncovered that the finished side it's been lying on for a month has now been damaged
Currently deciding whether it's going to be possible to sand that out, but it's quite a deep textured mark that it's left. The visible top one is the worst, but there are about 4 others. The only good news is that the paint is now back in stock, so if I have to re-paint then I can. But it's a bit soul-destroying to think the painting is finally finished and then get a setback.