Progress update! If I insulated the switch that was sparking, the second from the top on the 10 point relay (org/white and wht/grn), the 10 point relay would cycle the 10 point reel as you'd expect. I disconnected the playfield and the game would still shut down upon any activation of the 10 point relay, so the problem had to be in the back box or the main cabinet. It sure is helpful to be able to rule out the playfield so quickly!
Anyway, I started just looking for those wire colors in the back box. The wht/green was clearly routed properly and wherever it attached it was well insulated. The org/white lead back to the cut off lead on the match unit coil. I was thus confused as to how this could be a problem. I examined the wire routing closely and, at first glance, it looked fine. On the match unit, the two coil wires were tucked behind an un-used switch mounting bracket, so I went to re-position them only to find I couldn't move them. Reaching behind with my fingernail and prying a little, they popped out and there it was - the insulation on both wires had worn through and they had slightly arc-welded themselves to the match unit frame. I pulled them out of the way and separated them and started a game. The 10 point playfield switches now worked, as did the thumpers!
I'm hopeful the rest of the issues are simple adjustments and repairs now. One of the fuse holders is broken apart, a well known issue it seems. I am hopeful this is what's causing the lack of playfield and GI lighting except for the back box. The Bonus Unit steps up, but does not reset on game start. I need to check if it's resetting on bonus collect. And my now-functional 10s reel doesn't reset on startup but the game thinks it has. That should be easy.
Thanks for all the suggestions - the clue on the match unit was spot on - I just didn't see it right away.