If you don't want to reinvent the wheel you should contact TC DiBella, the owner of the Asheville Pinball Museum.

http://ashevillepinball.com/

He has a very successful business, started out as a sideline like you are describing.
So successful that after a few years he moved down the block to a much larger space.
On weekends in particular after the first couple of hours you can't even get in, it's always busy.
He has a phenominal collection of video games and pins, all are well maintained.
On the web site you can see his prices and hours.

If you are really serious you should consider making a site visit and getting some advice from him.
He's a very nice guy.