What delayed maintenance do you need to account for?

So should I use up a good chunk of heloc and minimize the hml cost.  

I had minimal experience with all of them.

Lots of online training and is well worth the minimal cost. 

House Hacking is a great way to minimize expenses, obtain property for very low money down, and learn the ins and outs of property management.

Both of these loans will normally require 20% down.If you are concerned about your primary rates, you could use an FHA loan to purchase with minimal down, live in the new property for 12 months, then refinance it or rent it out. 

If I’m buying properties for long term buy and hold, and am buying quality properties with minimal/no rehab, and with little/no cashflow (buying for long term loan pay down, equity, and tax benefits), is it hard to get multiple mortgages?

ADUs where there are minimal comps and obviously an ADU are sometimes far below the hands of cost.  

A 6-month delay on a 8-12 unit new build could cost you $60K+ in missed revenue.I'm not suggesting it doesn't make sense or trying to discourage the idea. 

Starting out, you're going to want to minimize those detracting factors.