1. Like that is going to work. The problem with that strategy is that Grievous' infrastructure is galaxy-wide. And any attempt to attack that infrastructure will be met with stiff resistance. Grievous can simply move his superior numbers around Revan's forces and hit him from all sides. Revan's only option is to spread his forces out to prevent that, but that means that his fringe forces will be targetted and eliminated.
2. Grievous has a company of Magnaguards with him, not to mention cruisers filled with Battle droids. And don't bring the assassins into this. They are just normal men (the non-Force user ones) compared to Grievous. They can't use their 'drain' ability on him as he has no strength in The Force.
Ventress is an incredibly skilled warrior and the Nightsisters are completely different from Revan's assassins. Not to mention that Grievous is incredibly difficult to kill (either straight up or from him running away).
Yes. Greivous has zero force powers. No precognitive abilities. A lone assassin could simply stealth right up to Greivous, wack him, and be done with the droid.