If Save & Quit is allowed (you save after the barber and clothes), why can't I just gather money AFTER the barber and than save BEFORE the first quest with Ian?

This is allowed, but you cannot complete graffiti missions to regain money, only hobo goals. You must also have the exact amount of money that you normally start with.

"You must also have the exact amount of money that you normally start with."

Oh, I thought that, if I just collect 750$ - THE EXACT AMOUNT for dino head, amjam, ship and so on, I could just start the run and don't bother collecting money in between missions

No, the money for story continuation missions must be acquired during the run itself.

Ok, thank you then for explaining :)

No problem man, hope you're enjoying the game!

can this be ran on a emulator like dolphin emu or anything in that kinda nature?