[RogerBW]

As I see it:

I. That depends on how much you de-rate your drive. One ramscoop produces enough fuel for one drive system running at full power; if the drive is running at half power, the other half of the fuel flow can be filling the tank. This should also deal with any drag you encounter. (At least in a universe where ramscoops work at all.)

II. The panel array can probably convert all the light that hits it. Other things will be up to GM choice, but focusing will be hard.

III. Universe-dependent.