So now that harry now has 2 kids to raise and protect, he is going to need capital. He might prefer to live a more spartan kind of lifestyle, but he needs a new place with a real threshold, and a decent nest-egg, could really be useful to him...

In that regard I've long been wondering why he does use Bob.
Bob is basically the equivalent of a super computer with an AI, we know from when he is living with Butters that he can operate a computer and surf the internet.

So why not have him use the stock market ??
feed him book on how it works, let him observe the market for a while, and then use him to daytrade or even long term invest if he wants to limit the access bob has to a computer. 

I know Harry can't have a pc at his house, but that's not keeping him from letting Bob operate one at ie. at Butters place.