Help! Im out of ideas

I am getting ready to take my brothers 40 gallon tank and I dont know what to put in it. I already have a 2 gallon, 10 gallon, 20 gallon, and 30 gallon. I own about two dozen minnows, 9 platy, 6 molly, two black mystery snails, two african dwarf frogs, one pleco, and an odd number of ghost shrimp, along with my two 4" Yellow Bellied Slider turtles. Now I have the two turtles in the 30 gallon, but if the 40 is longer then they will be moved to that tank. But, I want to plan on stocking a 30 gallon so that if I end up stocking a 40 gallon then I will have plenty of extra room. The only thing is that I dont know what to get into. I love molly and platy but I want to venture into a new fish that I havent had experience in.

Here is what I have had before:
Gold fish, angel fish, red tailed shark, neon tetra, and betta.

i loved having angelfish and might consider having them again but I want to do a small school of some kind of tetra and then have one centerpeice fish or two and then a few other fish.

I want to do more of a planted tank but with fake plants. I dont really like real plants because I will most likely have snails in all of my tanks at all times.

Any suggestions would be awesome, thanks. Oh and Maybe something colorful that doesnt get too big. Im clueless there.

Im not sure about loaches, I want snails in my aquariums and also I read that they would be most comfortable in groups of 6 and they get up to 6" to 12", so that would overload my 30 gallon limit. I like to do what makes my fish most comfortable, unfortionatly I dont think I would be able to go against any preferences of my fish. It is a neat fish though and thanks for the idea, ill keep looking.

i like that idea, i made a note of them. now for the other fish.

well, my pleco that i have is currently in my 20 gallon and i will be putting him in there. also having snails I dont know if I should put another "cleaner" in there with them. Although this is the last pleco that I will own. They may be cool, but they dont do anything after a certain point. Also I had a chinese algea eater and he was great, everything was spottless. Some reason he died and I dont know why, i think there wasnt enough to eat for all of them. There may be more in a 30 or 40.
Also I was thinking about getting a ram or two as my centerpeice fish, I dont know much about them, would a male and female alone be ok or do i need more.

By the way, thanks for your help and fast reply.

He is just a common pleco, he hasnt stopped working yet, but he will soon. The best way to catch a pleco is to "nudge" them into something gently. if he is small enough then you can get a cup and use your net to get him in there. Be carefull because they have little razor type things all over them. Or you could lower the water level and then they cant go up, only around the bottom. Make sure not to keep him in the cup or whatever to long because that is too small and he will start to freak out. They get scary when they need to be.