The two existing LTR units (on my family’s property) were built 5–8 years ago at a cost of about $80,000 per unit, so I’m estimating a 20% increase in costs for the new builds.My plan is to use the equity in the land as the down payment for the construction loan, which I expect will make closing costs the primary upfront expense.

If the lender is licensed in the state you're buying in, then they can do the loan.

yes, you could use the HELOC as a down payment on a hard money loan, and then the hard money loan for the rest.  

At first blush it looks like you're finance at $500k, so getting a loan for $375k.

You can get a normal owner occupied home loan to do this. 

If my spouse wasn’t opposed to moving I would try to buy a new house hack every 12-15 months and use low down payment owner occupied loans for as long as it made sense.

Bonus - the interest on the loan is tax deductible!

., the appraisal for 5+ is at least $2k-$3k) and the financing structure by lenders because Fannie/Freddie don't generally buy loans for commercial properties.So, for you personally, the biggest driver for the type of your next property is probably going to be the amount of a down payment/equity you can put in the property.

The expense tracker, reports and rental sheets (useful if you are planning to do the BRRRR method and need to calculate 2 different sets of loans).I used to have my own custom spreadsheets that I built but this one does everything mine did plus much more. 

I would suggest reaching out to owners of multi family who have no loan on the property.