Background and credit checks are excellent. 

By way of background, I have been working as a Medical Device Sales Representative specializing in orthopedics and total joints with Johnson & Johnson | DePuy Synthes.

If I technically do not have a primary residence, what would I list as a primary residence.

My background is in math and engineering so I also think it'd be cool to analyze their spending and maybe start recognizing areas for improvements. 

One San Leandro landlord is owed $132,000 in back rent and in Oakland you can't discriminate against rental applicants with a criminal back ground (except sex offenders) and several stories of non-paying tenants which took thousands in legal fees to evict in Oakland. 

That being said, for recordkeeping, it is probably better to have a different LLC for buy and hold vs flip properties - though you do not technically need to separate them or have LLCs at all. 

Not sure if that would technically be allowed.

Also, it would be great if I could get some suggestions on what website/tool to use to do background checks and e-sign lease agreements.  

Yes, probably 50/50 to start and then once you have a strong track record with them, you may have the leverage to try to get a higher percentage on your end since technically what you're doing is more time intensive than what they are doing (cutting a check).

Technically in AZ the renter can ask for last months rent back after they move in but most do not.