I also want to start building a network of sub-contractors including electrical, plumbing, painter, and landscaper. 

Note: Over the course of the 10 years I've lived in and remodelled the house, I had to do all the work myself so I've accumulated a wealth of knowledge and tools about how to do wiring, plumbing, roofing, drywall, tile, cabinets, etc. 

Plumbing, electric, framing things out may be quicker to hire someone but being it is a live in flip I am assuming you are keeping for 2 years for the tax advantages?  

Some places will take progressive pictures to be emailed to the code inspector and keep in file showing wires, plumbing and framing or what ever you are installing.

We did electrical, plumbing, kitchen, tiles, bathroom, and a firewall plus some miscellaneous items.

.- roof- HVAC-windows- major electrical- major plumbing- sidingIn general I don't look at unit turnover type issues as cap ex.

Older properties have cast iron plumbing which if well maintained are fantastic but the cost of repair or replacement can become very high.

GET and inspection and make sure you look at the foundation, the electric, the plumbing, roof, ac, water heater etc.

I used a company specifically for painting, a company specifically for flooring, a company for plumbing, etc.. if you would like a referral let me know!

There's also great books like the national plumbing,painting,electrical etc. estimators guide.