As far as mods go...
When I add something (like a lighted topper) to a pinball I never take power for the lights from the game's power supply.
I get 120V, and put a small 12V 'wall wart' power supply in the game to power anything that the game doesn't come with.
Lots of mods use alligator clips attached to the wiring in the game... I'm not a fan.
As far as what you need to do for your game...
When it breaks, fix it. That's about all. Your game will let you know if you have a problem. No need to anticipate what might fail.
(Note, this advice would be different if you had a Wizard Of Oz Emerald Edition, where I would suggest you buy a complete lighting 2.0 package and throw it in the bottom of the game for when you'll need it. It would be different if you had a 90's Williams/Bally game where I'd suggest having a couple of boxes of bulbs in the bottom of the game. And it would be different if you had a Gottlieb System 3 game like Stargate or Rescue 911, where I'd suggest a lot of fuses, lots of bulbs.)
