You need to be able to change keys in between tenants to maintain access control and the security of your property.

Here’s how I’m currently thinking about it:The interest rate on my existing property is 3.5%, so I’d like to maintain that rate rather than refinancing the entire loan.

In the latter case, I would still use QB to enter info provided by the 3P servicer and to maintain my general ledger for the lending business.

(Usually you cannot use prior employer history until you have been at your new job for 6 to 12 months, depending on the underwriter to show that you are maintaining the same level of bonus/overtime/commission income that you had at your prior employer).

It is important to find something that was properly maintained, with modern plumbing, electrical and roofing. 

However, I'm unsure about the costs of maintaining the SL in Spain, especially cause I read in some forums that these costs can be pricey..Do you have any views on the above based on your experience?

Your property is fairly destruction proof, costs near nothing to maintain, yet you can charge above market rents.If your property is nicer (class B) where the carpet alone might be $6k or more to replace when the tenant spills hair dye everywhere, you won't be as happy as in the situation above.  

If not, you could always maintain 2 separate IRA accounts, one self-directed for private lending, and then another for your traditional investing.

STRs also avoid automatic classification as passive if rented for seven days or fewer per tenant.To maximize tax benefits, maintain detailed logs of all hours worked on activities like tenant communication, cleaning, maintenance, and marketing.

What would be the best ways to familiarize myself with construction process, while still maintaining my W-2 job?