Kind of overkill though, there's really not much worth spending money on. The weapons are just skins with the exact same stats and you're just paying to unlock a gun earlier than it normally would. Good, if a bit cheater-y, for the ones that only unlock with 6-9 resistance levels, otherwise pretty much useless. You really only need one of each vehicle that has a weapon on it, which means buying a boat and maybe a helicopter since the free one only has 2 seats (and I think there's one with rockets). There's at least 4 trucks you get from quests with mounted guns on them so no reason to ever buy that. The free planes are the best ones too.
There's around 800 or so silver bars to be found in outposts too.
As for perks, I'd prioritize additional holster, the parachute->wingsuit->air drop line, grapple, leadership the moment you get 3 companions unlocked, sneaky sprint, locksmith, rifle and/or whatever other weapon(s) you like mastery, and the first couple health upgrades. Once you start raising the resistance level in some regions, grab black market and special ammo pouch so you can carry a good amount of AP ammo. Auto repair is really good once you have some of the weaponized vehicles, especially a helicopter. You're going to need human fish and fisher king for challenges at some point too. It's worth grabbing the leader perks for your favorite companions too, it drops the cooldown after getting them killed from something like 10 min to 3(?) min. Beyond that just grab whatever sounds good.
