Bought a protein feeder and it came with an internal funnel but the opening is fairly small and I feel like protein pellets would prob clog up at the opening. My question is how wide do y’all think the opening should be? This one is prob 1 1/2 in opening but I’m thinking it needs to be atleast 2 inches.

All will depend on how big the protein pellets you use are and what your consumption rate will be. 1-1/2” is probably fine but I would prefer it to be 2” -2-1/2” also.

Same issue with the funnel inside mine. I made the hole as big as I could and that seemed to help.

I like mine 3”. A jig saw with a metal blade works well to open it up.

3" min but 4" is even better. Otherwise you'll be cleaning out a clog and you don't want moisture inside because dumping one is a pain. I'm sure you've researched and know you do need some ventilation to avoid condensation.