I recommend using a hand held impact driver (the hit it with a hammer type). They are sold at most automotive parts stores for a reasonable price.
Yes, it is a good idea to replace the screws with allen head screws at your earliest convienance.
After you get the factory screws out, take them back to the auto parts store or your local hardware store to match the size and thread pitch.
Go with the white lithum grease, and be careful to avoid getting any inside the clutch. BTW, the clutch hates oil, so don't go that way.