Never invest in any city on this list of the 50 most dangerous US cities.Low operating costs: High operating costs are one of the driving factors for many companies, leaving states with high taxes, regulations, and other costs.

How long have you been investing yourself?

The data @Devin Conley posted is pretty solid from my experience (I do not know Devin nor how he sourced the data, just going by my own investing experience).  

But I’m thinking of getting into STR investment and become more active.I’m a complete newbie to short-term rentals (STRs) and eager to wet my feet in this area.

As far as I know, your assumptions about the tax implications are correct for non residents, it was one of the main factors that stopped the idea of investing in Spain for me.

I am in Tampa Florida so the investment market is huge here for both as well. 

To Sum it up, its a good idea if you can exceed the cost of capital (higher rate than your cost of debt) with what you earn on your heloc/debt you pull out and invest.The question is how much gains above is enough to substantiate the risk of your variable interest rate, well thats up to your personal investing criteria.

And would it be worthwhile investing to rent? 

I have an opportunity to purchase an investment property that is NOT ON THE MARKET yet.

I've done most of my investing out of state.