If there are lots of active rentals, then it very well isn't below market as there's substantially more supply than demand.

In which they dont even ask for SSN (I had to edit the application to supply that)?

If you got some special stuff your able and willing  to ship to FL please DM me.The special stuff goes to my regular customers at fair prices as you've noticed with the places you've tried.

And the recordings are updated on a regular basis. 

It's called PEX not Plex.If you are totally replacing the water supply plumbing, unless local code prohibits it I would say to use PEX.

If it is rated for a 3 bed, but it's not getting super regular use because of vacancy, then I don't know if I would be too worried about it.

Inspect your property regularly and hold tenants accountable before the problems get out of hand. 

With the supply shortage of great houses, you'll have to put more down to create that intrinsic property.Very rarely are physical assets, especially infrastructure, intrinsic from day 1 at the highest leverage available.

Tenants use to threaten to sue me or complain to authorities regularly.  

Kohler products can be purchased at Home Depot or any plumbing supply store.