I currently have a 20g tall that is planted fairly heavy and I was wondering if a betta be compatable with 4 serpae tetras, 4 golden white cloud danios, 4 bloodfin tetras, 4 cardinal tetras, and 4 silver tetras?
But even if your betta was amazingly pacifistic, he'll be constantly nipped at by at least a few of the tetras. Also, looks like a ton of fish for a 20g already.
Paradise gouramis are much bigger than bettas - both in length and mass. I have a plakat betta in with a female black paradise gourami, and she is double his size.
A paradise gourami could work, and so could a plakat/king betta.
Sure. I find neon tetras, harlequin rasboras, white cloud mountain minnows, and pencil fish to be non-nippy. There are other species which are not nippy, too, especially when kept in schools of 6. Looking back at your original list...it's mainly the serpae tetras that are the problem. You also have a lot of fish in there.
Personally, I'd aim for 6-8 small schooling fish (of one type), a betta/gourami/paradise fish, and call it good.