Well your water parameters looks good. Nothing to worry about there. If you plan on doing anything with plants a bit higher GH might be a good idea.
When it comes to the fish you have what I would say a pretty unhealthy mix. You cannot provide ideal conditions without some of the fish getting out of their "zone".
Your platies and molly need a bit higher Ph 7+ and the molly wants a little salt in the tank but the others do not. Your livebearers need a higher water hardness think around 10ish is recommended both for the platies and mollyies.
The other fishes does best at lower phs around 6-6.5 and softer water. Also your angel should get a tank mate and same for the molly, ottos are a schooling fish so two of them sounds a bit mean
I would recommend you getting your current stock properly taken care of before adding more. And consider returning or giving away the molly/platie or the others. When that is sorted out the most interesting fish are probably dwarf chiclids (if you decide to go lower ph and softer water), like apistogrammas or something. They tend to be rather aggressive, more so when spawning. So hiding places and not so sensitive fish are a good idea as tank mates.