In other words, you will pay less in taxes by reducing your taxable income.

Probably like any market, look where the new construction is happening.Look at what people are buying and what they are willing to pay.See if you can do it better, faster, cheaper and still make money.Then calculate the max you can pay for lots.Then go find lots to build on.I'd probably draw a big circle around DFW and buy on that circle or just outside of it. 

While revenue at 10% of total property cost might be a quick calculation to find profitable properties, there are other calculators that will provide better insights for you.

Lenders don’t like half finished projects, especially where the borrower “mis calculated” by $100,000.   

You diligence needs to be trying to pull out if your operator has some competitive advantage that will let them eke out marginally more returns for you, to more than offset the additional fees you are incurring.Of course, with a 1031, the analysis is slightly harder, because you have to factor in the tax savings you are getting through your 1031, relative to taking sale proceeds as taxable and investing in a group that may have lower fees.

The "boot" (cash or non-like-kind property you received, which is $190k in this case) is taxable.

One of the best tools out there is a blended rate calculator that can help you determine if HELOC or cashout makes more sense. 

They didn't have all the real estate books, blogs, YouTube gurus, financial calculators, etc.The best thing you can do is buy a house and educate yourself on how to manage it well.

What are good strategies or online calculators to help make rehab estimates? 

You mentioned it was 3% interest only however the math calculates to a payment of around $3950 a month if it is amortized at 3% and 30 years starting with a unpaid principal balance of $937,000.