Let's see... We're gonna play with the 1"/gal. rule because it helps get the general ballpark... although you can stretch it quite a bit, as long as no one level is seriously overstocked and everyone has room to stretch their fins.
I would go for maybe 4-5, maybe 6, regular size gouramis (golds, opalines, moonlight), and 3-4 dwarfs (Personally, I'd go with the fire red dwarfs instead of a giants, because I imagine they must be named giant gouramis for something...). That gives about 22-28" of gouramis at full size (the golds etc. grow to about 4"). Then, pick a barb, and get a decent size school of it, say 8ish. You can always add more or a school of the other barb also if the tank looks like it's got lots of excess space. Figure 2.5" per barb... that's another 20", so 42-48" so far.
I think, with all the bottom area of a 75g, you should be fine with a rainbow shark, group of yoyo loaches (4-5 might be a nice number, maybe 6), and a 6-8" pleco. That gives you about 70-82" total, which should be about right for a 75g and is well dispersed through all levels of the tank.
I honestly don't know how well shrimp or snails would fare. If you are trying to breed snails for the loaches, in the tank will not work out so well. They will get eaten faster than they can keep up the population. They don't produce all that much bioload regardless, so you can add them without worrying about them hurting your stocking level.
I would go for maybe 4-5, maybe 6, regular size gouramis (golds, opalines, moonlight), and 3-4 dwarfs (Personally, I'd go with the fire red dwarfs instead of a giants, because I imagine they must be named giant gouramis for something...). That gives about 22-28" of gouramis at full size (the golds etc. grow to about 4"). Then, pick a barb, and get a decent size school of it, say 8ish. You can always add more or a school of the other barb also if the tank looks like it's got lots of excess space. Figure 2.5" per barb... that's another 20", so 42-48" so far.
I think, with all the bottom area of a 75g, you should be fine with a rainbow shark, group of yoyo loaches (4-5 might be a nice number, maybe 6), and a 6-8" pleco. That gives you about 70-82" total, which should be about right for a 75g and is well dispersed through all levels of the tank.
I honestly don't know how well shrimp or snails would fare. If you are trying to breed snails for the loaches, in the tank will not work out so well. They will get eaten faster than they can keep up the population. They don't produce all that much bioload regardless, so you can add them without worrying about them hurting your stocking level.
