We will obviously ensure they carry proper insurance, abide by the law, and submit to regular inspections.Question: if they live in the home and operate a business, would you charge them additional rent for the business side?

You would want to call around to some local Property Management companies in SWF that do STR's and see what kind of rates/fees they charge and the occupancy you can expect.

I typically charge 1.5x a months rent for the deposit.

I may do a new roof ( I have a roofer will do good work and charge me a deeply discounted price - (close friend of mine) Of note and the last question is - the electric meters were not present and I called the elec company and they told me that the esid's were retired and the meters removed.

I usually see around $50-75/day charged to heat pool.

Be careful with the property managers, in my city they charge 12-15% of revenue, $500 annually for finding tenants and then there are additional charges for each maintenance call. 

If they submit to screening and pass, I add them to the lease and let it go.NOTE: I charge a fee for adding or removing tenants because my time isn't free. 

There are a number of factors to consider; how long your brother has owned it, value of the property, type of building and specialty options (charging stations for electric equipment, etc.), fencing and security systems, and numerous other factors. 

A PM is going to charge you to place a tenant , charge you to collect the rent and charge you to evict the tenant , then charge you to have the repairs done .  

How much are they charging.