These properties offer the opportunity to enter the market with lower initial investment, with the potential to increase both property value and rental income through rehabilitation efforts.

It is prudent to have 6-9 months of mortgage payment allotted as an initial reserve account.

So I would focus on no prepayment penalties (you didn't mention any which is good) and also maximize the flexibility on when you repay, whether that's a longer initial term or options to extend. 

We initially met with a couple builders my father has worked with previously and are currently awaiting for detailed breakdown of cost estimates.What would be recommended for taking out a loan for this build?

The only issue I can see by initially circumventing your agent could potentially be "cut out" of the deal and/or their commission when you do end up writing an offer because the listing agent could argue that your agent was not "procuring cause" for your interest in the property since you contacted the listing agent directly and began negotiations. 

Hi Magda..haven't visited Myrtle Beach in a years, but kicking myself for not investing when I initially had the inclination.

Then 95% of the time my contractor goes to the initial showing with me.

This creates two loan payments ($100,000 of equity and $300,000 on the new mortgage).Key NumbersHome Equity Loan Interest Rate: 6%Mortgage Interest Rate: 7%Rental Income: $3,000 per monthExpenses (management, taxes, insurance, maintenance): $800 per monthIncome and ExpensesMonthly Rental Income: $3,000Monthly Expenses: $800Monthly Mortgage Payment: $2,000ExplanationThe investor earns $3,000 in rent each month.They pay $2,000 on the investment property mortgage and $800 on other expenses.This leaves $200 profit each month or $2,400 per year.However, you have to pay $6,000 interest on the equity borrowed.This leaves you with an annual loss of $3,600.This example shows that while the rental property generates positive monthly income, the interest cost of borrowing the initial $100,000 results in an overall annual loss.

In the event you miss calculated your equity potential, you should be fully ready and able to settle the transaction or be prepared to lose your initial deposit. 

Thanks for the initiative!