Earthquake fault zones, flood plains, and high fire hazard areas are off-limits.

During the "fix up" process, you would use a different kind of loan that will end up converting to a DSCR loan once you have tenants living in the unit(s).So, I would need to use maybe a construction loan for the renovations and then convert it to a DSCR loan?

I would highly recommend getting your license for property management, and/or realtor.  

Bonus Tip: If this quadruplex is out of state, I’d highly recommend building a reliable local team (cleaners, handymen, etc.) and maybe consider hiring a co-host or VA to help with day-to-day tasks, especially if you scale up. 

There are numerous threads about sub to and many investors believe it is a high risk strategy (especially for seller) and believe buyers who use it “take advantage” of naive sellers.  

The end product will be great, as others have mentioned perhaps in other threads, Delta has not increased any of the cost, so there is still a huge equity upside.

The other quotes I received were often unreasonably high compared to other properties in my portfolio—sometimes exceeding my current carrier’s increased rate for this property while offering less coverage.

If you get in with a locked in company that's in it for the long haul, your success and being taken care of are gonna be pretty high. 

I paid about $1,500 for the installation of a high-quality 4-security-camera system, which can be monitored by both the tenants (and you!)

This was a highly successful transaction.