I would not get full sets to start, and the 0.3 are not particularly useful, IMO. Hard versus soft depends mostly on what you shoot, even horizons or broken horizons. If you shoot with the sun near the horizon, you are better off with a reverse ND grad. I think is 0.9 soft, is 0.6 hard, and a 0.9 reverse would be a good starter kit.

Question: do you want/need to use a CPL with your grad NDs?