Be debt free (in terms of personal finances), have good credit score, good debt to income, and go make good deals.

The HELOC/LOC is a good interm term loan as long as you do the long term financing as soon as possible.

Managing an Airbnb takes years of experience and even an entire team (in terms of pricing etc.) to really maximize everything.

here in Florida many of the communities with STR rival and exceed hotels in terms of on sit amenities, water parks, etc.

It looks interesting but i cannot find much on them in terms of reviews? 

san diego is the hottest market in CA right now in term of inventory drops!

One of the best investments, in terms of ROI, has been when I bought a duplex with zero money down as a Veteran.

I've also been looking at townhomes but I'm not as familiar with how they compare with a SFH in terms of appreciation and rental rates (definitely a weak spot in my education). 

Some people treat their STR like a hobby and others treat it like a business.You don’t know the numbers are based on if owners use it 3 months a year themselves, or manage it themselves and have STR knowledge or farm it out to a competent or incompetent property manager.In one area I invest in, the biggest players are all large direct booking sites with hundreds of properties so their revenue doesn’t show up on airDNA, etc.Use conservative numbers and understand your skills in terms of getting a property to be unique, marketing, listing management, etc. or the competency of the PMs you are interviewing.Good luck!

All your question is answered in basic calculator.Your question is what's difference between 3 +5 and 2+7 ; they're all good product if used intelligently can be very profitable.Fact is , 30Y above 6% rate would not have significant difference in term of balance payment compare to 10Y I/O if you sell the house in year 5.Please do note that 10Y IO and 10Y ARM is vastly different.