for substrate, honestly, I would suggest just doing dirt capped with sand or some gravel that you think looks nice
do you have a background? and as far as diy co2 it won't help much on a tank that large.
as far as lighting goes, catalina makes great lights, but I don't know which one to recommend seeing that you don't want to go hi-tech
as far as stock, I really like your list, but I feel like you still have room for more if you so desired.
I'd definitly increase the number of ottos to at least 8, simply because you can, and same goes for the amano shrimp since you won't ever see them in a 75...my 10 has like 8 and even then I rarely see them around.
I'd also consider nerite snails of some sort, like 12+, since they are very good at eating algae. Perhaps also consider getting a nice variety of cherry shrimp, though I get the feeling that cherry shrimp and rams = full rams and no shrimp....so thats something to think about.
If anything, I'd get the cherries and then let them breed for a few months before even considering to add fish, otherwise I say try some other sort of invert. Bamboo and Vampire shrimp are rare, and would fit in a tank of your size. I bet that CPO crayfish might also stand a better chance with rams than cherry shrimp, although CP are also a ton more expensive.
You have tons of options considering you want smaller fish and have a relatively large tank