Yes, crispy/rough foods do promote healing - and to my amazement, dd ate crisps when she would eat nothing else
Avoid orange juice or anything acidic/citrus: stings like crazy. dd went off milk anyway, I think dairy tasted downright weird (though hard to tell, she was barely 2 at the time). Rice bread for toast? Nothing that might stick to his wounds, nothing too gloopy...
I think dd at ham at times, toast, ice cream, a few crisps, and biscuits
There were entire days when she would only 'eat' ice lollies - and ice lollies, as opposed to ice cream, were good from the very start: they hydrate kids who don't want to drink, apart from anything else.
Seriously, do not leave hospital without a prescription for pain killer suppositories unless your ds is great about taking meds, and has taken them with no trouble after the op. You can't reason with such a little one, or even bribe, if they're in pain. And some GPs, oddly, are reluctant to prescribe them - ours did, but others I know had trouble getting them (maybe cost more??!?).
As for the loud bit, I wouldn't worry - I think that was just dd