I'd suggest calling around places that do HVAC *and* plumbing.

Assuming that the basic infrastructure is already in place, meaning I don't have to add on to the house, I can get in and out for less than $10k including adding/moving plumbing.

As a plumbing contractor there arent many hand tools that I dont personally own.

Keep in mind, this all started with a small leak in the basement plumbing of a very old house:Tenant reported she could hear a leak in the basement when she did laundry. 

I genuinely enjoy doing carpentry and minor plumbing/electric, so I did much of the work myself.

Upgraded electric, new plumbing, HVAC, new kitchens, bath etc.

This is really important in remodel when using an unlicensed contractor especially when there unlicensed buddy is doing electric, plumbing, hvac etc.

The property management company has had to make a few minor repairs (plumbing and HVAC).

A true scope of work outlines everything -- cabinets, trim, structural work (including engineer prescriptive) if removing load bearing walls, plumbing changes, electrical updates, etc. 

It has an apartment that is rented out in the back and an attic that is plumbed for an apartment addition, so there is an income producing aspect to it even if I purchased it as a primary residence.My question is can I purchase the property with a partnership LLC (which already exists and owns property) and then rent the main house from the LLC for myself to live in?