I took out a conventional mortgage because it was the only access to cash I knew how to get (but I’m not sure if I can keep doing that honestly, lender was pissed I sold in less than 3 months), all in (repairs, closing costs, holding costs, new roof, etc) = $78k.

According to data I've read, home prices in the Orlando-Kissimmee-Sanford metropolitan area have gone up 12% annualized during this period. 60.9 - 12 = 48.9%.Does this mean that my rehab improvements improved the value of the home by 48.9%?

Let's assume I only have access to bank lending (please don't give suggestions saying I should find people willing to invest, I'd like to stick to a bank for now). 

You separate the holding company for a number of reasons: rental income is taxed at a some of the lowest rates, and the risk of loss is different in character than that of running operations, its tax filing looks different (as a business) than a business that runs operations (deducting capital improvements, etc.), among others. 

It seems pretty straighforward and a sensible question.I'll be investing starting in August when I have access to my employee 401k, which I will roll into the Solo 401K I have set up.

Access to an attorney will become very important as you consider this move.My preference is a C Corp but an S-Corp is also great.

At the same time, you can be improving your personal finance position to have a solid foundation for investing and taking calculated risks. 

Moral of the story is not to store things in places that are accessible to tenants.

My situation is that I had set my eyes on this house which is only accessible through Hubzu.

I can't imagine a more frustrating and dangerous scenario than to try to invest in an unfamiliar area that meets your financial proformas but where you don't know anybody, have access to on and off market opportunities, have relationships with trades people and property managers.