As for finish work I know exactly what I will be using and shop that myself, hiring people to do installation (tile, flooring, plumbing fixtures, lights, etc) Southern California is such a large area, with subs and suppliers spread out over miles; and having an easy way to bid our stuff makes it more convenient for everyone. 

I am trying to schedule a sit-down with my suppliers and see if they can help fund my projects, currently, I have a record with them but those are not credit transactions, more like cash before delivery.

How do I protect myself from liens from my contractor's subcontractors and suppliers?

The other issues are secondary things.Shop around or ask local investors (that you meet at the REIA or here on BP) for a used(if on a budget) appliance supplier.

In fact, when I started rehabbing, I had absolutely no construction experience, so this was my first major lesson.Of course, there will be materials that we have to get from other suppliers; in some cases, we can do something similar and in some cases we have to go to the stores to pick things out by hand.

Do you really want to teach your kids the principle to invest based upon the hope of "future earning potential" or the reality that W-2 income DOES NOT keep pace with inflation or commodities pricing, is the hardest earned, highest taxed income available to a person and beholds you to 1 supplier of income?

Call local suppliers / lumber companies and ask for recommendations.

You should be more concerned about releases from subs and material suppliers.

Given that their roofing prices are pretty competitive with the cheapest suppliers in the area, the $200-400 in rebates make this the lowest priced materials solution I've found.

Or Vis-versa, the contractor will give you a deal for buying the product from their preferred supplier.