Or should I put in the 720 day holding period, remove holding costs from calculation and remove my "typical rental rate" from the mortgage cost as well as put the 2018 projected price?

Good luck working with a bank on funding requests and draws, you may find yourself financing the construction for periods of 14-30 days until bank approves on a draw.

Although there may be other certificate holders/lien purchasers, sometimes they do not file for the deed/foreclose on the property prior to the statutory period/date, as required. 

Looking to get insights into the vacancy rates, especially during the non summer periods as well as to understand who would be a typical customer (families on vacation, singles etc.)any an all insights, are most welcomed Thanks!

Get the loan docs for the HELOC and see if it allows for the draw period to end and the repayment to start.

Again, it is only active for a set period of time (I'm pretty sure it is 7 days) and anyone with that link can access that file.

If it is their money you should not have the right to decide on your own to make a purchase period.

I looked into the right of redemption period in NC, and it stands at 10 days after the end of the foreclosure sale.

Sorry to hear so you are dealing with so much in such a short period.  

Real, substantial success versus using say a 10 day inspection period.