Correct me if I'm wrong but Fluval 120 is 120L or ~30G correct?
Plecos - unless they are BristleNose - are a definite NO as they will quickly outgrow the tank, my 4" *baby* is now 15"
Angels too will outgrow your tank - If they are not crowded growth is
Dime size - 1 month
Nickle size - 2 months
Quarter size - three months
Half dollar to silver dollar size 5 - 6 months and up to 3-4" at 1 year.
Haven't kept Dwarf Gourami so can't speak to them.
Not a Barb fan so can't speak to them either.
will be useful in planning just how full you can stock your tank but even it is not full proof so use it as a tool to help decide then come back here for more *hands on* advice.
I'd definitely return the pleco, forget about Angels Gouramis & Tetras and up your barbs & loaches into schools of 6+. Maybe add another variety of Barb if you have room