The Cokin filters, in my experience, have a very minor color cast. Maybe not. It's not bad at all. Even the cheapest grad filters are usable.
The hi-tech filters don't have a color cast, but they are transparent to IR. That means for some films (fast color negative, velvia 100, others) they'll produce a magenta cast. For properly manufactured digital they shouldn't. Possibly at high ISOs with newer sensors, though. With the red camera they might be a disaster...
The Singh-Ray filters, at least above two stops (three stops and above), have an IR dye and are color neutral across it and the visible spectrum. Pretty cool, but possibly unnecessary. You can custom order two stops with the IR dye, too.
I'd get two stops soft. Three stops hard is useful, since sky and reflection are often around three or four stops apart, so you'll get a nice symmetry to shots of the ocean at sunset. But the look is too pronounced and kind of cheesy, imo. I have a lot of respect for anyone who can get by without any hdr or grad filters, but if you choose to use them I'd go two stops hard/two stops soft. If you like a dramatic look three stops is good, too. The "reverse" ND filters that fade in two directions look really cool, if very special-purpose. A three stop reverse filter might be really cool.