Get replacement cost hazard insurance along with an umbrella policy of at least $1M, probably double in your area.

So i put in an offer for 10% down conventional loan, $530,000 with 10k back to me for closing costs and it was accepted right away.

I want to know is it more cost effective or easier to purchase the property alone and put it in a mortgage in our name or purchase the LLC from him that holds the property within it.

This will increase the return above what can be obtained on a passive investment.The flipside of having the power to control everything is that it can be alot of work (and a full-time job if a person is putting in sweat equity).

(after I deduct all the labor/material costs). 

Housing prices are high, mortgage rates are high, and competition is fierce so revenue is way downIt’s one thing if you bought a while back like many of us did, so your cost basis is much lower.

Is just the fact that no garage could be a no go for some buyers enough to build it even if it only raises the value by the actual cost?

If you don't want to finance the other projects then you should consider your opportunity costs.   

Specifically, the cost to have it corrected is now a known material fact. 

I manage 400 rentals and the most significant claim ever filed was a kitchen fire that cost $20,000.