Until you have a clear idea of the direction you want to go, it will be difficult to find the right mentor to guide you.

I can agree that finding comps for a triplex would be much more difficult than SFRs in the same area.  

I am wondering whether it is better to save up cash  (will take longer to do) to use toward a down payment or use equity in my primary residence for the down payment, then take out a 2nd mortgage to finance the balance on my investment property.

What I don't understand is if the homeowner is about to foreclosure - why don't they sell their home, pay off the remaining balance, and pull out their equity?

Too many parties that can potentially make your life difficult.

You have to make sure the person or company over the association is not siphoning money and is also being a good steward of the funds balancing the budget and tracking repair items.Special assessments could kill your cash flow model.

However, as you said, this may be market specific and in some markets the purchase price is so high vs. rents that it may be difficult to House hack and make it worth it. 

Hopefully @Dave Foster will chime in if I’m wrong but my understanding is you’ll be taxed on cash you keep or any lower balance mortgage you obtain.

I'm usually very wary about partnering with a contractor, seeing as how I got screwed over by one at the beginning of my real estate career that took 2-3 years to recover from.If you own the lot free and clear, it shouldn't be difficult to get financing for 100% of the build costs (feel free to PM me). 

Difficult to advise base on sketchy information provided.