I'm not really good at diagnosing problems like this without my hands on the machine, but Problem 1 sounds like it could be jones plug related, or if you have a schematic, check for a relay switch that might cut the power to the playfield lamp section, and of course check the blades on the tilt relay.

Problem 2 I would look at the 1 point relay, make sure all the blades are making good contact and are clean, and then the contacts on the score motor that pulses that relay to give you the 5 points.

Unfortunately there are so many variables, it's going to be tough to even know where to start in trying to diagnose. EM repair is largely trial and error, at this point I would probably remove the playfield and try to get the game to start and reset without it in, that way you've eliminated some of the potential problems.

You should be able to get the game to at least try to reset either by the start button, pushing in the hold relay, manually turning the score motor or resetting the main relay bank.

I have my Showboat set up at my shop, next time I am there I will grab the schematic, then I'll have a much better chance of helping you.

I was just talking to a friend, he reminded me that he had a fairly similar problem on his Showboat, and it turned out to be one of the switches on the trough release, so I would check that but be careful as I believe 120V goes thru one of the contacts.