If you're planning to hold and rent it out, you can refinance  to get a better rate after some months. 

What I plan on doing is using heloc for downpayment and renovations (10-15k).

You may want to plan for an exit loan just in case. 

Our plan is to sell or refinance within 15 months targeting a sale price of 3.5 million.This property is two blocks from the beach.

I just started my career in the U.S. military and am hoping to have my first assignment in Europe, specifically Germany.

The only time you can't require a specific 2x or 3x income is if the renter uses subsidized vouchers.

They'd like to keep it, but can't, they have other debts, so much going on, but now they have a plan.  

I'm planning to have a separate bank account/accounts for my entire portfolio, just wondering if anyone has recommendations for software to use as someone who'll have buy-and-hold and will be working with a property manager?

My best market to sell them are through attorneys doing business and estate planning.

Our parents paid 10K for the plans to build it in 1975.