I found
this thread had heaps of great information!
I Soft Pawed by cats a few days ago and it went really well. I got the kitten sized ones for Lily who is about 4 months old, and the small sized ones for Stumpy who weighs about 7 lbs.
I found the kitten ones a little big still, so trimmed the ends of before I stuck them on. Maybe put one on your kitten without the glue to get an idea of how the sizing is, then trim and apply.
To actually Soft Paw them, I put the glue in all 10 caps for one cat (we did front only), my husband held her, but she wriggled a lot, so he scruffed her (while supporting her body weight), and she stopped wriggling. It was really easy to just slide them on. I trimmed their claws regularly, but for the couple of sharp ones, I just trimmed the ends before I put the Soft Paws on.
My husband also ended up putting her down a bit so she could support herself on his lap, while still being scruffed, and gave her Gerber baby food while she was getting the paws done. That's her favourite food, and she was quite happy to sit there getting treats while it was being done.
When they were all done, I squeezed them all to make sure they were sticking, then put her down. In hindsight, I should have spent more time ensuring they were all completely on, as one of them is only halfway on, but glued super tight, so isn't coming off. It's not a big deal, but it looks silly, and I'm worried it'll get caught on something.
Lily, the kitten, was easy as well. They went on without a problem, and she got baby food treats as well. Stumpy was actually trying to get at the baby food while we were doing Lily, so I don't think she was too traumatised by it

Lily was shaking one of her paws when we put her down - I think I got a bit of glue on her. Otherwise both cats didn't care at all, and I haven't seen them try to pull them off.
They still "scratch" on the scratching post - I assume they like the stretch as much as anything. Lily had been clawing up the bed rather than jumping, so had a rude shock when she jumped halfway, tried to claw up the rest of the way, and slid straight off the bed! She learnt she had to jump the entire way very fast though and has stopped trying to claw her way up everything already.
Here's how they kind of look on my Stumpy.
