A male betta with any of the fish we have discussed is a No. Bettas are far too fragile to be housed with semi aggressive type fish and most larger fish like Cichlids will end up eating him/her. Bettas are best kept either as single individuals, or with small peaceful fish (I keep my male with three white cloud mountain minnows) but you can also keep them with neon tetras, platys, any small peaceful fish (no long flowing fins though, so fancy guppies are not an option).
Have you tried searching Youtube? Many people post videos of their tanks and if you type in "125 gallon fish tank" or something to that extent you can see what others have stocked their 125s with. However because we all know there are many , shall we say, not so knowledgable fish keepers out there, if you find a few combos you like, or a few species from diff vids that catch your eye, make a list and then do some research on those species' behavior/size and once you reach a decision about what kind of combo you'd like, post the proposed stocking list here and see if others agree in your choice of a combination. If an overwhelming number agree its a decent combo, then start stocking. If many advise you to swap out certain ones or change the lineup entirely, best to heed the advice instead of having regrets later on.