I’ve found properties on the retail market (MLS) by moving quick and efficiently, but I focus more on and finding properties on the investor market (through auction, wholesalers, and more).What Services Do I Offer?

I replace everything so I can get the higher efficiency for my tenants.

There are honestly many ways you can really go about but if you are looking for the fastest and efficient way, I would also agree that you should partner with someone who's already flipping homes in your area.

New shingle roof - $6-8 per sq ft New high efficiency furnace and all new duct work with 8 reagiters - $5000-7000New high efficiency tankless water heater with new 1" gas line. $3500-5000New hardwood flooring with stain - $10 per sq ft. 

Should I sell for the gain and go into another renovation or is there another method that would help build cash more efficiently?

Most likely they are going to get a move out notice so we can perform rehab efficiently and they are welcome to apply for the unit once we are done, however they will be screen properly just like the rest.

There is a turnkey vacation rental in Hawaii I am looking to buy.  The home includes furniture and a passenger vehicle. The deal may require the vehicle+furnature be transacted outside escrow. Do I maximize the value ...

Does anyone have any suggestions on being as efficient as possible with this?

It's going to be LOOONNNG time before a 3d printer can quickly and efficiently print a $250,000 house. not much demand for a $5,000 house.

Basically they are installing solar electrical on their fix and flips during the rehab process, getting a wholesale price on the install, keeping the Arizona Solar Tax Credit for themselves (since they owned the property when it was installed), marking up the house by the retail install price (which they have no problem getting in this seller's market), and then using it as a selling point as the house is now energy efficient.