I quickly bought one piece of property for each character when I was able to do so because I wanted to see what that was about. I later did my first assassination mission and I learned about buying stock in the competing company to potentially double your money.

I completed two assassination missions and got 50% and then 80% gains on the stocks. I got several million dollars spread across the 3 characters, but I'm thinking I should just save my money and keep doubling it on assassination missions. I believe heist missions can also have the same effect since we're stealing from a company.

Should I buy stuff as soon as I have the money or should I save it till I can buy everything? Is it risky to have so much money on hand in case I get wasted and have to pay the revive bills?

Correct me if I'm wrong, but isn't the revive fee capped at $5,000? That's nothing to worry about in the grand scheme of things.

I'd say don't worry too much about min-maxing your money. That doesn't sound fun at all. Take Reggie's advice and just play the game.

The way I see it the whole thing is sorta messy. This is gonna be sorta spoiler-ish, but I assume you were expecting that.

Firstly most of the properties are really only there to give you side content (so saving them for the end means you have to binge story then side content), secondly you get a ton of money at the end so you can pretty much buy most of it (and the stuff you can't buy is way out of your range either way) and thirdly I'm not really sure if it's even possible to save the assassin's missions untill you actually hit the big score.

In the end I don't really think it matters at all, it's more like one of those situations where if you've played through the game once and know exactly what happens then maybe if you optimize it you can get some of the more interesting properties earlier. The best advice I can think of is buy the most expensive ones you can afford, in my experience the more expensive property, the more interesting it's feature is. And as mentioned, saving them for the end only means you have less freedom to switch things up.

There aren't a ton of assassination missions in the game. Unless you really want to buy that golf course ($150 million!), spend that cash.