1) there is definitely hype around 70s Gottlieb titles. They go for significantly more (on average) than the others.

2) BG quality is more important as stated by a few others.

3) I think deal breaker comes down to your abilities and what you can repair as well. Some of the guys on here can rebuild a pinball machine with their hands tied behind their back and a thing of dental floss as tools. Some of the guys don't like touching up paint, others do work Like Picasso. Comes down to preference and what your end goal is with the machine. I can't do much besides turn the damn thing on, so I like the machines to be in better condition just due to my skill level.

4) can't comment much on this.

5) totally depends on the game and your timing. Otaku buys everything for pretty cheap comparatively. He is successful at it because he is patient and isn't out there expecting to get NIB looking Gold Strikes tomorrow. I think this comes down to timing/ patience, what titles you are actually looking for, and your abilities around fixing a machine. He's a good example of being able to get some pretty nice EM machines without spending a premium dollar, just have to be prepared to wait.