I would say it is not good to be a one trick pony. Each game has its nuances and strategery. Knowing how to play them well will make you a better player. For instance, TOM will not help you learn to make a side flipper shot. It's pretty hard to Shatz an inlane if the game doesn't have one. etc...

Very dependent on money. But I agree with clubber if you can get multiples do. Variety is king in pinball even more so then cash. Variety is great for skills and fun; almost any game will get stail if you only have the one game.

I think the choice is "more games or fewer."

Substantively, I think it would be good for starters to find a few games (2-3?) that have a good shot arrangement/variety and conventional flipper layout. Then work on the 2 basic, fundamental, essential skills: ball control and aiming. Doesn't matter if the game is simple or 'deep'; just practice the basic skills (bounce passes, dead stops, drop catches, etc.) and hitting specific shots, regardless of point value. After that, you can get to know different games and work on strategies. It's good to first be able to generally hit what you want, and then you can learn what you want to hit on different games.