Okay I have just finished restoring my 1980-1990s falcon lazer, but I am not sure how hard to pump my tires?

Tyre says min 100PSI so will have to be above that and I like my tires on the firmer side but as I understand it Higher the PSI the more prone to punctures they are?

I live in crappy UK and the roads go from mediocre to crap so what would be a good PSI for Average to Poor roads?
(I was thinking 120 to start with)

Sorry for NOOB Q its my first road bike XD.