Anxiety of first dog owning

Hi everyone, New here. I just wanted some advice on what I can do.

Recently adopted a cavoodle puppy. I have been having a lot and lot of anxiety and stress over it. I have had the questions “was this a good choice?…” “should I have done this?” “What if he gets separation anxiety…” “why can’t I get breathe….?”

I’ve just been going about my day as I usually would, we have done a few small minutes of crate training, he’s been doing okay with the toileting (has been going outside) but has had a few accident inside (which I know is normal) I’m worried as he’s not been eating, I have been trying to encourage him too (it’s his second day for us)
First sleep went okay and I am worried that tonight won’t be the same

Any advice