For tetras I'd say go with some glowlight or cardinal. Or perhaps some of the black ones?
Sand: I prefer it, it looks sharper in a tank and gives it a more realistic look (to me at least).
Filter: Get a HOB, they're easier. Aquaclears are popular, but I don't like them (I found them kinna loud) Whispers are good filters (by Tetra) My personal fav? Millennium 2000 It's what I have on my tank at the moment, I'm not sure if they still SELL them (I got mine with the tank from craigslist) but it's a quiet filter and it's WONDERFUL.
With Ottos, be careful the last few I've gotten have been kinna sickly and ill... Get a school of them, they like to school as do Corries. Ottos will clean the tank up good.
Also, sand will be great for corries... It's soft on their barbels...
For a centerpeice fish, no clue... I'd personaly go with a HUGE school of tetras