Depending on the task, a GC should hire subcontractors. 

Of course, with all things, the answers to all these matters will depend on the circumstances.California tends to have more laws on the books and requirements and restrictions that it can be a good idea to form a CA LLC for out of state property so that you as a CA resident are covered, and to try to have your contracts fall under the purview of CA courts.

What is considered good or bad for a vacancy rate? 

If the seller is open to seller financing, I was thinking of putting in a full price offer with 10% down and maybe terms of 30 years with 4% interest rate.  

I did a cursory internet search when they contacted me and the relatively high ratings and apparently legitimate business structure made me unwary of them being dishonest.

Might be some options but will depend on a number of details here. 

The decision to acquire additional properties depends on your financial goals and management capacity.Continuation of Strategy: Continuing to acquire properties and utilize cost segregation makes sense if you want to offset W2 income.

Then they will sell you a 5 year warranty for 10% of the discounted rate.

We have approximately $475k equity in our primary residence (2.5% rate for 11 more years - $850k value).

Regarding turnover: This depends on whether you have them sign a 1-yr. lease, Semester lease, 10-month lease, etc.