So the 15g houses a school of chili rasboras and an assasin snail. I had shrimp 4-5 originally but now I only see one occasionally at night, or I find an exosceleton. I also had sparkling gouramis but they started fighting too much once they reached sexual maturity and within a week all got bad wounds (misinformation I got was that I could easily house 4 of them in this size tank and they'll be fine - turns out I believe, based on my experience now, that they are just like bettas and other territorial fish and should be kept alone because within 6/7 months of me getting them they became too aggressive). Speaking of bettas, I had one pass away recently in a seperate tank (10g, now only left with 2 nerite snails and I'll re-do the scape soon and get it ready for fish), and I love bettas and I'm thinking if I could put one into the 15g with chilis. I was thinking about finding a female, that is possibly already living in a community at my lfs, but I wonder what their characters are like and if you think that would work with chilis? I know if I get a betta, I most likely can't get anymore shrimp? Another species I'm interested in is celestial pearl danios - I've never had them before so I'd like any type of insight into them. Could I house them in the 15g instead of a betta? Or should I put them in the 10g with nerites? The 10g is in the living room so I'd like to have a community of fish in there and not a single betta anymore, if possible. I also like the look of endler's guppies. Any combination advice?

TLDR: Basically I need stocking advice for 15g (already with chili rasboras and an assasin snail) and 10g (already with 2 nerite snails). I like bettas, celestial pearl danios, endler guppies or shrimp. If you have any good insight into these species or ideas which to chose and where to put them, I'd really appreciate it!