You really don't need to buy a kit.
Firstly go for a Polariser. No question!
Then ask yourself if you want to do those long exposure water/sky shots that have been so fashionable recently. If you do then you'll probably need a 8 or 10 stop ND.
Graduated ND's are really useful for all sorts of landscape work. Why not just start out with one to see how you get on with it? You don't even need a holder, you can just hold it against the rim of the lens, moving it carefully until you see the effect you need/want. This may be a bit tricky without a tripod but it is possible. As to choosing which one to go for, I started out with a 2 stop hard grad, then got a 1 stop as well. The latter is excellent for getting natural looking skies in conjunction with the polariser. If I was getting a soft grad, which I may eventually do, I would probably go for a 2stop.
edit : I see you want dramatic skies.....maybe a 3stop hard grad then? First find your sky, though........