I purchased a home last year and the insurance company (Allstate) contacted me a few months after closing stating they did a random drive by and my roof didn't meet their standards and I'd be dropped from the policy if a few minor issues weren't corrected. 

Also, if you ever want to scale up, then you have to train good tenants and keep everyone to the same standard.

Loaning to your LLC sounds like the better way to go since it's the one buying the house and you keep all your costs in a business entity bank account so it's easier to track and deduct.  

SFR from my perspective works best in a lot of post industrial towns - Chicago, Cleveland, Philadelphia, Baltimore - where rowhomes proliferated lending the stock an even greater level of standardization than most apartment building have internally along with a very low cost/unit and an outsized ARV on a refinance.

Is my situation pretty standard or is it just bad luck?

My first questions would be, are they installing "solar shingles" (which I would not recommend) or a standard solar system with the installation of the roof.

I am myself a landlord and I wonder what can I “reasonnably“ deduct from the deposit.

If I pay them interest on the loan ,do I get to deduct that interest when taxes are filed?

There is no "standard" fee for this. 

Cons:You might be held to a higher standard as a licensed agent in a transaction that goes awry.