Their insurance and mortgage interest rate may or may not be accurate depending on who you use and your own financial situation.  1. 3% Annual Rent Growth - Is there a way to verify this?

As mentioned above you could just act as lender and record a mortgage/deed of trust with promissory note and personal guarantee from all parties in the deal would be the cleanest way to structure the deal.Another option which could potentially yield higher returns on your money is to become an equity partner in the deal, this could put your money in a riskier position and in the case of a default or failure to perform of other partners. 

My current builder has been not performing on a project I have and it is clear they are not doing anything to change their posture and improve or make up schedule.

Having a poor understanding of business, contracts, state and federal laws, negotiations, maintenance costs, etc. will continue to result in poor performance and finger pointing on both sides of the table. 

Is the data on the deal accurate, and do the facts support the fundamentals of “your” kind of deal?

Areas like LA and NY will have higher materials and labor costs compared to places like NC or TN.You may be ghearing $350 pSF and that may be accurate for new construction here in LA, but likely for homes around or under 1,000 sf.

Their work performance sucks. 

Plenty of books and websites explain this **** and usually pretty accurately yoo...

I haven't gotten in there just yet to really see what its all about but reading through reviews and seeing what it offers I see that it can and likely will be a simple yet powerful, and accurate way for me to account for my business.

BRRRRR's always have a limit to the amount that makes sense and thus are difficult to accurately predict.