You are aware of the pH issue, but of more importance for fish is the GH (general hardness). This is the dissolved mineral in the water, and this can impact fish in various ways. The GH and KH (carbonate hardness or Alkalinity) also impacts pH, so we should find out the GH and KH first. Your pH may tend to lower naturally, depending upon the GH and KH. You can find these out from your water authority if you are on municipal water, check their website; no need to waste money on a test kit.
Second point I'd like to make concerns shoaling fish. I don't think anyone has yet mentioned that while we are sometimes required to consider minimum numbers, with all shoaling species they will be better with more. Cories for example live in shoals numbering hundreds and even thousands sometimes, so if you had say 7 it would be much better than 5, and so forth. When selecting a shoaling species, get as many as you can (generally determined by, or relative to, the tank size), within reason. Given your tank dimensions and volume, I would suggest a group of no less than seven cories, up to nine or ten.
I agree that combining different species is not the same thing as all one species, with any shoaling fish. However, with cories you do have some latitude which you would not with most other shoaling fish. For decades I have maintained cories in multiple species, some of them only one, two or three of a species (for various reasons) and provided they are together, they seem to manage well. When possible, I acquire five or six minimum of a species, but sometimes this is not possible, hence my mix of species. I have some species in pairs (just happened to be a male and female) and they have spawned several times; but they are in a tank of 50 cories of 11 or 12 species.
To your list of fish. No serious issues, but some things to consider. Bristlenose must have real wood in the tank; they digest this and it is essential for the health of their digestive tract (so far as we know, they do not derive any nutrition from eating wood). Cories would like lots of wood too, they love hiding places and grazing wood surfaces for the microscopic live foods that it supports. But wood is essential for BN.
The tetras mentioned are all quiet, sedate species, with the possible exception of the rummynose, but these are not over-hyper. Barbs are, so combining these groups is not as good an idea. Rasbora tend to be quiet fish too. And by quiet and sedate, I mean they are not active swimmers, but more cruisers or even just remaining together without much movement. It is best to have either active fish or sedate fish together, as the combination is usually not going to work. Sedate fish can become stressed by hyper active fish around them. The cories are fine for this, as they are not up in the water, and their comical bumbling around is not really a threat to anyone.
The Golden Pencilfish (Nannostomus beckfordi) is generally peaceful, but males are territorial, very much so, and prone to nip fish that "bother" them. From the species you've listed, I don't see problems. But if for example you were to consider hatchetfish in future, they would not fare well with this pencilfish species. I have more than once had to move my group of this pencilfish because they continually nipped fish that approach the surface, like hatchetfish, even otos. However, this is a good species with lower water fish--and all of your listed tetra species are fish that prefer the lower half of the water column--as the pencilfish will remain in the upper half. Another thing, back to the activity, is that this pencil is much more active than its cousins.
Knowing the GH and KH will help you/us pare this list down.
Byron.
Cories are some of my very favorite fish... which, of course, is why I've kept them with so many different species. I can't think of a time in my fishkeeping life that I had a tank that didn't have cories in it!
