new to fish keeping

Hi everybody, i'm relatively new to fish keeping. We got into it as i promised my daughter some fish...after a few months of hunting and deciding, my OH and I decided to keep tropicals as marine would be to hard for us as newbies.

we were also advised against live plants as we were noobs. So we settled on a Fluval 125.

we also decided on a community tank.
1st question is how many fish can we keep in a 125 litre tank?

currently we have a pleco, 6 scissortail Rasbora,2 platies, 11 neon tetras, 3 rummy nose tetras, 3 mollies..everyone gets on great and the scissortails have adopted the 3 rummy nose into their shoal and they do everything together..lol

due to their size are tank still looks pretty empty.
2nd question. Is there any big fish we could put in that would not bother any of the smaller fish?

and lastly,what other fish would you suggest for our tank..

we enjoy sitting staring at them for hours and our daughter loves them!

thanks in advance for any help