So the initial appraisal for the refinance was good at the time, but now the As-Is is not gaining traction with buyers.

By working for a larger corporation you are gaining an unfair advantage, by letting them train and develop you (while you are getting paid) and you do real estate on the side.This idea is not from me, read RichDad. 

Are there other, more cost-effective alternatives to gain similar support and knowledge?

But this will also lead to future inflation.The issue is going to be the rich will get richer as they can live with lower cash flow but gain appreciation.

The foundation was already approved, permitted and finaled years ago for a 3400 sf house, and its solid and I won't be building directly on the overhang edge; but rather back away from the edge a few feet to prevent any load issues all the weight will be on the longer sides of the existing footing.

Hey, if you get married you'll be able to shield an extra $250k in capital gains!!

Being a curious person, I gained an interest in real estate investing due to other classmates being interested in real estate.

To Sum it up, its a good idea if you can exceed the cost of capital (higher rate than your cost of debt) with what you earn on your heloc/debt you pull out and invest.The question is how much gains above is enough to substantiate the risk of your variable interest rate, well thats up to your personal investing criteria.

Make sure this enough gains to make it worth worrying about.

Yes you are losing out on market gains but you are gaining appreciation on the property, cashflow from rents, tax benefits, etc.....