Looks like I have everything all figured out eh? except for the following of course

Tank mates: This a breeding setup so I will only be keeping two species. The and a school of some form of characin to give them a relatively realistic dither. I would prefer to skip the neon and cardinals, for whatever reason they have very little appeal to me. Im thinking either black neons or glowlight tetras but if you guys wanna throw some more names at me that enjoy black water or vote for the current ones that would be great.
Quantity: How many adult would you recommend for a 55 gallon? Dimensions are (LxWxH) 48x13x20. Personally I'm thinking 7 or so.
Ratio: How many boys and how many girls out of the amount you think is appropriate for the tank size. I was think 3 males and 4 females but open to suggestions.
Substrate: More a question about colour (light or dark) than anything else but unless told otherwise I will probably go with a fine grain.
Let me know what you guys think
Regards
James