Does anyone know the figures for these expenses offhand possibly - Vacancy Rate, Capex, Property Managers?

It shouldn't be a problem to call and while I don't know the specific rules for Hawaii (probably something like a smoke detector in or next to every bedroom and a carbon monoxide detector in the house), rules regarding smoke detectors are not going to be "grandfathered in" (a term that building departments hate btw).

Currently, the houses in that area are renting, but they take longer to rent. 

Usually helocs are adjustable rates, so the rate will come down as the interest rates go down.  

Follow-up question: if I hold the property after having bought it under the LLC's name, wouldn't I be subject to commercial rates instead of consumer rates when I go to refinance the construction loan into a permanent loan?

Mortgage rates started to drop last week and they are looking much better as they trend down.

People told me I was an idiot to put a sauna at my mirror house and it CRUSHES.

If outdoor: open field or hoop houses? 

I've already bought the property because I was afraid of rising rates (got a 3.4% thank goodness because they're literally in the 7s now), but it's still costing me 1800/month before construction starts.

The "exchange rate" for conversions of tax deductions to tax savings vary from investor to investor.