My plan was to follow @Brandon Turner's "Stack" method and acquire a property each year to build my portfolio.

Depending on your method, I'd steer clear of this direction.

I ask them for the best method of communicating (email, text, phone call, letter) and put that in the notes.

I've heard from numerous investors that great tenants are worth their weight in gold.

Which method costs the most?

This is actually how we got started BRRRRing and it is also my favorite method. 

Hello Memphis BP, I just wanted to share that I finally completed my first BRRR deal sorta.Purchase Price: 76k (I bought this property from a rehabber in 2019)Purchase Method: CashMonthly Rent: $1,150Appraisal: 190kCash out Refi 120k (minus 7k for closing cost plus points) cash in hand was roughly 113What I learned during the process: Important to show income on your taxes I have a W2 so not having my properties on my personal w2 did not kill me but if you're a full time investor trying to not pay taxes or showing properties as a lost may hurt you when trying to refi. 

Whats a couple good methods to determine local storage unit vacancy rates to analyze the need for more units in a market?

However Deferred Sales Trust are one method of doing this.

I wish to try out this method, instead of just being a landlord.