.- Margin on the AIO ranges from 3.25-3.75% + 1 month libor Index (which has lately been around .16% or so).

I don’t have anything rare/super risky, mostly broad market index funds.

I wouldn't think too big and just go safe in index funds.

If the Fed does what is expected your indexed rates should start to decrease on these productsI always prefer local over Mega especially if you need financing in the future a relationship is more  valuable than shaving a couple bps @Kyle Kline

.- The rental yields in premium zones of central Madrid barely reach 3.5% - 5% gross due to government policies, such as the rental index imposed by the socialist government.For these reasons and many more, I'm considering investing in Miami.

I use real estate and index funds to diversify.

However, rate would be prime + index + an additional +2% for the shock factor just to qualify, but you can draw the funds whenever you want vs cash out where you have to draw all the money after closing. 

“The problem is that in 1997, when the maximum exclusion levels were added to the tax code, they were not indexed to inflation,” says Evan Liddiard, CPA, director of federal tax policy for the National Association of REALTORS®.

-What does the rate float to - what is "Margin + Index"?

Winston sits at a 2 out 100 on the crime index (with 100 being the safest).