I began investing on my own, and managed all my own properties while working full time.  6 single family homes was pretty easy, provided great additional income, and I had more than enough time to focus on my career.4) Excel is the standard for creating models. 

They would tell you to go to PC Richards and call them with a model number for a price.

I bought mine in the recession, so got steals, and was able to pull all my cash and then some out with the BRRR model. 

The numbers might look good on paper but the maintenance, repairs, turnover, and vacancy makes the model not work for most investors.

I also have only researched single family modulars the multi unit models may be different.

I know repairs differ from property to property, but what's the ideal cost for repairs in the BRRRR model? 

At the very least you need an experienced commercial retail broker or also a commercial retail attorney to help out.Have you gotten a soft quote for debt with a capital markets mortgage broker and modeled out a return scenario over a 10 to 15 year hold?

You will not get money for the unit you live in, but put the market rent that you could get in your model.

Use a price per square foot model- Light rehab $15/sq ft - Medium rehab $25/ft - heavy rehab $35+/ft (these are very loose guidelines)2.

Zillow's business model is different than the other big competitors and is more dependant on the market.