Congrats on getting things under control

. I think some casualties were inveitable to be honest.
Just taking a look at your current stocking
1 powder blue gourami (2 inches)
2 gold gouramis (4.5 inches each)
1 pink kissing gourami (10-12 inches)
1 striped gourami (2 inches)
1 tiger barb (2 inches, but aggressive and nippy)
1 black skirted tetra (2 inches also prefers to be in a shoal)
1 clown loach (Could eventually reach 12 inches or more, slow grower tho.)
1 pleco (Like you said, gets to be big

)
1 black mollie (6 inches, prefers salt in the water)
1 dalmatian mollie (6 inches, prefers salt in the water)
1 orange mollie (6 inches, prefers salt in the water)
1 rainbow shark (6 inches but a very active swimmer needing lots of swimming room)
Is there any chance you could arrange with your lfs to trade some of the fish back in for more suitable tank mates ?
I think your tank is about 30.25 inches x 12.5 inches x 18.75 inches in size, personally I'd consider 4 inches as large a fish as I would put in that tank. You could probably get away with a bristlnose plec which gets to about 5-6 inches long since they aren't that active swimmers.
If it were my tank I would look at swapping out the Kissing Gourami, Tiger Barb, Clown Loach, Common Plec, the Mollys (because of the salt preference) and the shark. Possible adding more black skirts to take the shoal up to 6 or replacing that with a shoal of other smallish tetras. Try and get a Bristlenose instead of the common and maybe look at Khuli loaches instead of the clown. Your tank is a decent size and there are lots of fish that are suitable for it, you just seem to have chosen some of the larger ones

. If you want to have something like the mollies you could consider platys which have similar colours and only grow to about 2 inches.
Please don't take this as criticism, we all know that your first tank is a learning process. Then again, if MTS takes hold and you decide to get yourselves a 120 gallon to let things grow into you could always consider this one a grow out tank
edit : grr... I *still* don't know why it adds 3 lines instead of one when I hit enter....
