I guess that depends on if you plan to have a league night as well but....
If your going to do pins, and want to attract more business, I'd say you need more like around 10 pins
But start with what your budget allows
I'm sure you have a certain amount you can realistically spend
Maximizing you bang for buck is going to be important
I'd say a blend of old and new is a must
Get a newer stern with a. Theme most can relate to
A few system 11 games, like high speed, pin bot , whirlwind or taxi,
A few DMD games, this can be tricky , do you go with a list games only ? Personally I'd get one a list game and 2 or 3 b or c list like fish tales or junk yard
And at least one em game in good repair
Something for everyone!