If you're going to take on the mantle of a carer, I'm afraid you've got to be prepared to take the knocks as well as the triumphs, so "Be strong, grasshopper!"
[Sorry, I obviously watch too many films/TV...

]
So glad to hear Spikey's back in Town, but then again, when he goes walkabout once more (as he inevitably will), don't be too downhearted.
Nutkin sounds like a weird sort of hedgehog, not eating meat. I take it you've offered him/her 'proper' meat, not just meat-flavoured biscuits etc? Odd, but interesting!
I think you're right not to dive in and abduct the fellah/lass for weighing just yet, as there should be a good month or so before conditions start to become touch-and-go for hedgies' weight - also it'd be a betrayal of faith if you put him/her off (what may become) their cosy new des res.
As Ian Hislop said on HIGNFY recently, "you don't fatten a pig by constantly weighing it".