This should be an awesome tank when finished
My 2 cents
Go for either asia or south america. There are subtle behavioural differences, which lead to fish not getting on so well because they misunderstand each other.
As already mentioned in a tank fish do not shoal too tightly. So for a great looking tank you would have only one (!) shoaling species (excluding the bottom dwellers here) but in a very large group. Maybe you can go for two, if they are as different as possible in size, shape, behaviour, and tank location they use (more surface or bottom oriented).
Think twice before you introduce a species to your tank which might breed! Kribensis are great fish, but they breed very rapidly and very soon will overrun your tank. Same holds true for Bristlenose Plecos if you introduce a pair.
You need to start with more snails
MTS are very good and additionally I would recommend ramshorn.
Use sand as substrate (mandatory if keeping Corydoras)!
Edit: Just forgot to mention: if you go for SA there are small tetras of which the males are territorial, they would very well suit your setting and could be kept additionally to the shoaling species you chose. I especially have in mind:
Nannostomus beckfordi and
Hasemania nana.