Cherry barbs will be fine. I don't know about ghosties off the top of my head, but I have kept them at various temps without an issue as well though. You have some definite differences in temperature preference, so you may have to wing it and try a few things to see what works for you (after all, not all heaters are all that accurate in what temp they keep, so you may have to fiddle a bit). Gbr are often kept at like 80-82. Though, you may be ok lower since you only have 1 and are not trying to breed them or anything. I can't picture a gbr really doing well long term at anything under 78 though, so you sort of have to pick your battles.