I wouldnt suggest using grievous as a main hero and unless you plan to play hvv exclusively you'll need to get used to playing as all the heroes. Every time you can get a stra card that increases health or health regen use it and for lightsaber heroes use star cards that reduce stamina drain. For grievous theres a card that gives extra damage to thrust surge and one that increases damage after one enemy hit with claw rush so those are the two I like best for grievous. It really depends on personal preference though.
Line Up Weaklings, of course. In every gamemode. for the other two, run Sith Trained and Beating Heart in Trooper Modes and Play around with other ones for Hero modes. I usually keep this same setup for any gamemode I play as grievous though. Grievous is probably the most enjoyable Hero in BF2 Nowadays so good luck with your leveling up!