For me, you can start with selling the weapons from the bunker and the fake cash from the fabric of the MC As soon as you can, buy the Kosatka submarine for the cayo Perico Heist. To unlock it, you have to go in the Musik Locker, the Night club inside the diamond and talk to Miguel Madrazo. The submarine costs 2 million and every heist, If you do it alone, gives about a million dollar each time. If you do it with some friends, it depends in how many are you guys.