I plan to do some value add by increasing rents(which are well below market currently) along with some capital improvements then refinancing within the 3 yrs.

At the minimum - your bank statements (2 months), any mortgage statement with balance, HOA statement if any, 2 yrs of your complete tax return with w2,, all trading and retirement account statement (2 months), and 2 pay stubs, your SS card and maybe even your state ID.

I am guessing your are Active Duty Military also, which means that you will likely only spend a few yrs or so in the area.  

After another year and for the remaining 15 yrs.

My exit strategy is refi 12 mos later, payoff HML, continue to pay on seller 2nd for 5-7 yrs, do another refi and cashout seller and then I work towards paying off the long term mortgage. 

The landlords there have been buying homes for over 30 yrs, so they know what they're talking about.

Can you afford flat to negative appreciation over the next few yrs?

The goal is 1000 plus units before I am 40 yrs old.

Yes those tenants will also move eventually, but if you can increase your average tenancy from 12 months to 3 or 4 yrs you'd probably make out ahead.

My portfolio is just getting started as I have a home in Chandler that I purchase 3 yrs ago where I house hack with my brother and another one of my friends.