What documents do they require, what credit scores do they allow, how do they verify previous rental history, etc.?

The only example I can think of is that I asked an applicant questions about their credit report.

Credit Union, Brokers, Banks (all have different advantage & disadvantages). 

Depending on local regulations, you can mix up STR/MTR/LTR. 2) Get systems in place in those exact cities; 2 PMs preferably via NARPM, 2 high quality inspectors, and rotating book of handyman, 1 lawyer, and a credit union contact for leverage along with investor friendly nationwide lenders.

Quote from @Charles Fay: Hello all, first time posting and wanted to ask for your advice.currently in the military awaiting a 9-12 deployment within the next 6 months.I will have ~150k savings after deployment, 85k before, with no debt, payments or anything other than basic bills, 750+ credit.

Have about 50k I would invest (access to more), with excellent credit and good income too, from my full time job.

Leveraging a HELOC (home equity line of credit) could allow you to invest in multifamily without completely draining your savings.

What documents do they require, what credit scores do they allow, how do they verify previous rental history, etc.?

We purchased this as a BRRRR on a Line of Credit, went to do a few fixes then refinance.

We consider background checks and credit checks only good for 60 days.