The property requires significant rehab and I am considering to put in a lower bid than the asking price.

Managers cost so much and make repairs cost even more, I do not see their value until you have 50+ units and no time. 

I’ve heard about ‘gap funding’ for fix & flips to cover down/closing/holding costs in addition to the hard money loan for most of the purchase price & rehab, but how realistic is it to secure that type of funding?

Can't recommend @Joseph Cornwell enough, he helped me buy my first duplex in Cincinnati and he has a contracting business, so he can give you advice on repairs, remodel costs, etc

renter sucked...didnt pay.... cost me a lot of money blah blah blah.

This will be used for repair cost and down paymentAny advices going forward?

Consult with a Financial Advisor: Seek advice to navigate negotiations and explore refinancing options that best fit your needs.By taking these steps, you can work towards lowering your interest costs while keeping your loan terms unchanged.

I am looking to see if anyone has any suggestions on how to get an accurate number on rehab costs.

Partner Driven financed the Owens Creek Rd deal using its own capital, covering the $250,000 purchase price and $20,000 in renovation costs.

In short , any rate/currency hike is causing liquidity crisis causing delay in ground up project even for project that was approved 2 4 years before the rate hike…. plus build costs/  profromas run 3 to 4 years ago are wildly in accurate