4montj - desensitising

First time cat owner. Picked up our 4 month rescue this weekend. While she lets us pet her around the face, and pick her up sometimes, I want to desensitise her so I can cut her nails , put on a collar and give her a batch. I’d love to be able to give her belly rubs or hold her like a baby but I’m not sure if she would let me.

Any advice would be greatly appreciated.