I brought in 2 GCs for estimates before the offer and it would have made a small profit - around $25,000.

As a roofing contractor, if I need to quickly give a rough price estimate a good rule of thumb is 1/3 materials, 1/3 labor and 1/3 profit.

If I need to get my license and wait a year to form my own brokerage/LLC, then I am willing to do that.I have estimated the expenses to be between $800 and $1,000 for the licensing, the education course, and exam(s) [might do FL, AL, GA and/or TN for license].

I dont have an accurate rehab estimate (had two contractors see the property and one gave a blanket estimate of $150K). 

GAAP only really makes sense to public accountants and financial analysts.

I paid 90k in May 2020 and current value is estimated at 150k.

Hoping I could get some suggestions on how best to get estimates of ones property and which site seems to be most accurate.

Do you understand how to estimate the true ARV of a property? 

There are many wesbites that will estimate a job by zip code.

Also, of course, make sure you read Millionaire Real Estate investor, The book on estimating rehabs, Long-distance real estate investing just to name a few!