It will be tough to qualify without a lot income to show but it will depend on the loan size (you might not be able to do FHA 3.5% but you can put more down to lower the loan amount and improve your DTI).

I haven't been ordering materials for a few months but wow!

What materials are going to give the most back to me?

This is a tough subject, as there are many wholesalers out there but most are not great at what they do.

HELOCs are tough on rental properties. most banks will only loan them on a OWNER OC property. give some banks a call on the island, I would be interested to hear as well. 

Of course, if you run a slumlord and have black mold everywhere and sewage backing up, etc.. that liabilities on that lawsuit get pretty pricey, especially I'm guessing there must be a clause in the insurance policy about owner negligence (granted thats tough to prove to my understanding).

A class is a tough market because renters are generally too stingy/saavy to pay the rent you need to get to make it work.

The BRRRR method there is a bit tough- even "fixer uppers" are priced just about as competitively as turn key homes and I'm sure construction costs to rehab are sky high.

Please share any thoughts on changes to your strategy with the cost of building materials through the proverbial roof?

It will be tough but you can do it.