You will need to decide if you want a shop that has a lot of training, or if you want a small boutique shop, or even a flat fee brokerage. 

I'm the mindset that it's better to own fewer high quality properties than lots of inexpensive ones (e.g. all those roofs, HVAC etc to replace in the future). 

Normally the tenants understand.If you're having consistent issues with a tenant abusing the HVAC only (if they are abusing other items then it may be helpful to find a new tenant), I know some HVAC companies offer an annual plan with a certain number of visits per year at a flat fee.

Its not uncommon to see 2/1s in avondale on a 3 flat at $1100 each and you go in do cosmetic updates and bump each unit to $1900-2000.

Why would you give them free rent with they still have full access and use to the stove, refrigerator, walls, closets, flooring, roof, garage, lawn, etc.?

You don't need an inspection to know the age of a roof.

If the roof’s age is unclear, it might need replacing soon.Electrical systems can be tricky in older properties.

Many carriers have ceased offering new policies or will only accept properties in very nice condition with verifiable updates to the roof, electric, hvac, and plumbing.

I would say look at the big ticket items, roof, foundation, electric, plumbing, HVAC and assess from there if anything needs to be done 

He eventually put a new roof on my building and did an excellent job!