Head over to bank rate or and take a look at the mortgage calculators, plug in the numbers and get an idea of what the property needs to generate to satisfy the intended debt.You still have to underwrite the deal for the non-finance expenses as well(typically 40-50% of the gross rents). 

Or at least what are investors looking for today as far as return and cap rates?

You can find out nightly rates, occupancy and amenities.

Those sounds like great rentals and vacancy rates have been decent - our management team only has a handful of vacanies out of the 300+ we oversee, thankful for that.

If you're $400 below market rate I'd give them chance to "catch up".

What is the interest rate on the HELOC?

You can likely do this with your savings rate (that will likely increase) and age. 

Sometimes they’ve already negotiated solid group rates.

Tax-wise, profits are taxed at your ordinary income rate, and frequent flips may subject you to self-employment tax if classified as a dealer by the IRS.

With a fideicomiso, the gross income is taxed through a withholding tax whereas, with the corporation, the rate, you can deduct expenses but the taxation rate is higher.