120VA = 1 Amp

250VA = 2A

500VA = approx 4.5A

The 1A will work but you might find the flippers sluggish and bumpers lack grunt

2A is where you want to be, game will work well

4.5A this will run maybe 3 games well depending on the vintage.
 If the step down is a plug in type then run a multiboard to it and plug 3 games in.. you can have it as external then.

But basically, if its to go inside the machine then 500VA is money down the drain as 2/3rds of that power will not be used..
Just to add VA = WATTS.  In other words Volts X Amps, so a 110V step down at 500VA is 500/ 110 = 4.54A