Why not just do all sand? It's a heck of a lot easier to maintain than half and half. I had looked into doing half and half myself but it won't matter what you do because eventually that gravel will mix in with the sand, especially since Dwarf Corydoras like to play in it (I also have them and love them), they kick it around sometimes as well. I find Sand a lot easier to clean as well since you only have to vacuum the top portion, sometimes you'll vacuum up sand but it will just fall back into the tank if you pinch the hose a minute while siphoning. But eventually you get used to it.
And it's up to you which ones you want, I personally have 6 Dwarf Cory cats and 1 Bristlenose pleco as well as driftwood for her to munch on. Also each do something a little different. Cory's are scavengers and will eat anything on the bottom from pellets, flakes to wafers to veggies. Plecos and Otos do similar things where they eat algae but I believe they eat different kinds of it, as well as bio-film. Cory's are also hardier than Oto's which is why I chose them over Otos.
My girls go after any wafers I put in there, so I usually break one in half and then in half again and just put in the two pieces. I usually feed them a few NLS pellets while I throw in the wafer bits for the cories but they eventually find the wafers and take them away from the cories. I don't feed wafers every day though, it's usually every three days or so. And then I alternate to flakes and Omega One, letting most of the flake bits sink so the cories and pleco can get at them. And then everyone fasts on Monday and Tuesday because I'm not home :) But I always feed a big meal Sunday morning to hold them over.
and as far as those plant packs go the Amazon Basin plant pack is nice but I really like the Tropical Paradise one, little pricey but it's got some great plants. Just make sure you've got "high" lighting. I don't know the exactly wattage it is to have high lighting but I'm sure you could post that on here somewhere to get an answer.
Have you ever checked out ThatPetPlace.com? It's got some great plants packs and more than Petsolutions. Just an idea or future reference, it's literally where I get all my stuff because they're usually cheaper than the rest. Here's one that similar to the Tropical Paradise one but much cheaper: http://www.thatpetplace.com/jungle-a...gallons-234087
and more plants I believe. But here's all the others if you like: http://www.thatpetplace.com/aquarium...s#!plant-packs
(Sorry for the long post >< I can get overzealous sometimes)