We hold a unit vacant for one week and then expect you to start paying rent and utilities after that, even if you don't intend to occupy yet.

( I was thinking delray, boynton or lake worth) 2 - what are the added cost to take into account for str (hotel tax and cleaning and utilities right ?) 

I'm thinking that you're maybe dealing with similar to Indy weather, so I'll tell you one bush here that works well year round and what most of our utility companies (at least back in the 90's and 00's) had running around electrical boxes in front yards. 

Would tapping into our equity ($400k) on our primary residence utilizing a home equity loan be too risky for our first investment property purchase?

I'm a New Jersey investor and I've been utilizing the "subject-to" existing strategy for about 3 years.

Or if I should refinance later and utilize a different loan down the road?

They have to do special assessments to pay utilities.

As of today, they've only received 2,500 applications, totaling $5 million in rent and utility assistance.

A SFH shouldn't have any utility expense

If the numbers make sense, you could try renting it for $X plus utilities and then bill them separately each month for another $150 to cover the utilities which are part of the HOA.Reality is that is about $100K of mortgage.