It is really hard to say without taking it out, cleaning it off, and looking for damage. The bottom two (on the right side of the photo) certainly look repairable as the damage appears to be limited to the transistors. As for the row that is completely scorched, it is a little harder to say. It certainly looks like there was a fire and the board itself may have been heat damaged to the point that a repair is difficult. The traces certainly were subjected to a lot of current and heat and they may have delaminated from the PCB.

It is probably repairable depending on your time, motivation, and skill set. It isn't too hard to find System 3-6 driver boards, and a lot of people repair them. Since you said you haven't repaired stuff like this before, it may be your best bet to send it off to someone that would want to spend the time on it (many people may not want to even mess with it) or look for one that is already working.

This is true. I'd first try barakandl or HHasse here on the forum to see if they'd want to mess with it or if they have anything to sell you as a replacement.

Those last pics helped seal the deal in my opinion: this one is a gonner. A good one to hand on the wall in the garage to show as an example why you don't overfuse your game.