It seems like there are multiple military bases which is a good possibility for rental market, but just want to hear from the folks on the ground of how easy it is to find renters, and what area I should be looking at.

Most of those projects are fairly easy, heavy on subcontractors. 

So using that as a rule of thumb, if you have about $150-$200k invest you can definitely see your goals met depending on the market.

The numbers and construction for me is the easy part.

However, you cannot buy controlling interest in that LLC or even more than 30% of it (not sure about 30% but there is some guideline about it).You cannot also take any role in managing the project as it would violate IRA rules.

Is there a rule of thumb for how to go about securing deals like this?

Search 2% rule for example.

As I said, I've never done this, so is there a "rule of thumb" percentage of vacancy that I should go by?

It generally has easy to access comparables.

Website gurus don’t usually know these rules and the advice offered by some is just plain bad.