He's doing fine today. His testicles (or testicular area, since his testicles aren't there any more) look a little pinker than they did yesterday morning, but that's possibly just because I guess they have to be shaved for surgery.
His still has plenty of appetite. He's eaten two can of cat food so far this morning, I'll put a third one out before I leave, and he's got dried food and water.
I'm letting him wander around more of the house now, the hallway and landing, the bathroom that's been his domain anyway, and the kitchen and small utility area.
I'm keeping him out of the bedrooms and living room, because they've got more stuff in them, have more items which could be damaged by a cat pissing on them, and which aren't so easily cleanable. There's nothing too much in the rest of the house which can't be cleaned or which I'd worry too much about being damaged. It's not quite as tidy as it ought, but so long as he's not too stupid, he won't bring a teetering pile of crap down on his head (OK, so he's a cat, so not always the brightest, but he'll just have to be fast on his paws!)
I've put a second litter tray downstairs, so he's got an upstairs and downstairs toilet, which is better than me!
Most of his stuff is still in the bathroom, the cat bed, scratching post, original litter tray, toys, food, and drink. He'll also revert to the bathroom if he's feeling nervous, like earlier when the machine which eats kittehs vacuum was out. It seems sensible to leave it all there for the time being, so not everything changes at one go.
Whilst he could still make a mess (it'll take a while for the effects of his hormones to wear off), he was getting so plaintive and desperate to get out of the bathroom, that I've let him room free(er). I can't really blame him, the bathroom was a bit sterile and boring. It hasn't even got a window you can see anything out of.