The only correct answer:
"To Infinity, and beyond!!!'
Actually, it depends upon how much you can afford in a couple of ways.
How much can you afford in purchase of the machines
How much can you afford in storage/presentation space for the machines
How much can you afford in maintenance/upkeep of the machines
In a commercial setting, I have a friend who services a pinball bar. About thirty machines. He spends all day Wednesday every week doing service on the machines. Then he returns on Friday with the parts he needed on Wednesday and spends half a day to a full day Friday finishing up. Twelve to Sixteen hours of weekly skilled labor to keep about thirty machines in good repair when put in front of the public.
Before I sell a used machine it takes me 20-40 hours of labor to properly service it, before I put it on my showroom floor.
On my showroom, it seems that for every six months a machine stays plugged in for people to come and play it before they buy, I'll spend a couple of hours. Gottliebs will need re-bulbing every year, there will be burned out bulbs on every pinball that uses them, minor mechanical problems, even if the number of plays is very low. This would probably be less in a home collection that is only plugged in rarely, but it's still something to consider.
I knew a collector in St. Louis who had a goal of collecting every Wurlitzer Jukebox model ever produced. He got them (as far as I know, all of them!), and all of them were working. After five or six years, he was pretty unhappy. Every time he went to play his jukeboxes there was some machine out of order, and the constant effort to keep the machines in tip-top condition had caused all the fun to drain away from his collection.
I can assure you that it takes a heck of a skilled pinball technician to keep a large collection of pinballs in perfect operating condition. Hugh Hefner was a pinball enthusiast, and he spoke many times about the close relationship he had with his pinball technician. Whoever does the service on your extensive collection of pinballs is going to be spending enough time with you to become family.
So, it comes down to affording how much money and time in your life you are going to spend on this hobby.
If I won the Billion dollar lottery, I'd probably have a truly substantial collection of machines. Short of that, I'd need to see what I can afford in all the ways I'd need to afford for my collection.
