They have to do well with neon tetras I have 6 but thats the only fish I have in the tank right now and they are very healthy happy and active.
I also need a few bottom feeders or a cleanup crew. I would also like colorful fish that are fun to watch and dont grow too big

thats hard they absolutely can only be a little bit bigger than your neons. i had 5 they all got attacked several freshwater species that are always friendly to each other. The neons have tha hardest time staying safe

I have always been partial to African jackknives. They are black with a white stripe and medium sized eyes. They are long and skinny and move around a lot. They eat blood worms and are non aggressive. They do well with any other type of fish.

Along with them fresh water fire eels are cool. They also eat blood worms do they help clean up the mess that the jackknives dont eat.

Albino catfish make for good bottom feeders. All white with red eyes are cool.

Enjoy.

Larry

almost anything it depends on whats available so long as you provide plenty of hiding places. i would make a larger school of neons to begin with from there on i would slowly add large schools of smaller tetras such as:
penguin
sepae
lemon
black neon
bleeding heart
you can also add a couple dwarf gouramis or balloon rams

Black knifes are awesome I agree but I dont advise you to get them unless youre willing to lose those neons. Neons I find arent amazing tank mates they get really tail nippy : For bottom feeders go with ottos or cory cats buy 10 of them you have the room and both are social fish. Id suggest getting more tetras or other types of schooling fish for your tank as well actually add up the inches on these theyre small enough to work for the inch per gallon rule. You have quite a wide variety of choices for a 100 gallon tank but I dont advise you to get any fish that are large or agressive such as an oscar. Go with lots of schooling fish and maybe a few peaceful medium sized fish. Plecos are great bottom feeders too though one might be your limit. GL with setting up your tank and have fun buying all those fish