If I opt not to do it and just go with the pump there will be maintenance requirements for it and I'll have to rely on the tenants not doing anything that will compromise it. 

I lucked out and found a great cash flowing 4plex, but it was an off market buy and required months of negotiations.  

However in my city a permit is required to list on Airbnb for 30 consecutive days or less.

I plan to manage the bookings and do cleaning in between clients, so I will meet the "substantially all" materially participation requirement.

Having $30k-40k can be tight when you consider the down payment, closing costs, and other expenses, unless you qualify for a VA loan.Remember that if you don't qualify for a VA loan, most properties with assumable loans will require you to be VA-approved, as sellers don't want to lose their entitlement.

@Ryan SweeneySince a Solo 401k plan does not require a custodian and because you are looking for checkbook control and lower costs, you might want to inquire with a plan provider that is not a custodian or a trust company.

Also are appraisals always required I know that some companies used BPOs.

By my understanding, Fannie/Freddie requires that you "intend" to live in the property for one year.

California Civil Code Section 1710.2 Well, it's required, but it's not:"No cause of action shall arise against an owner or his or her agent or any agent of a transferee for not disclosing facts pursuant to paragraph."

in addition, if you have a flow of off market properties, these often require work and/or have risk, they typically have better cash flow than the MLS market.