There are so many ways to configure your tech stack but I value simplicity and efficacy. 

If you are doing a major re-design (addition, re-configuring exterior windows/doors/etc) I would consult an architect or someone who is an experienced rehabber (not a decorator) A well placed window for balanced light or thoughtful layout is the difference between a decent house and a great house.

The other 12 vacant are the same configurations (bed bath).

In other words, depending on your lot and existing building configuration, it may be more expedient to build an ADU and/or JADU, especially now that state law streamlines the permitting and reduces or eliminates fees. 

But I did find Insightly to be fairly easy to configure, free for now, and covers all of my basis. 

Which room depends on the way the house is configured and the value of the room - master bedroom gets priority, for example. 

They are around 400 SF and come fully furnished (appliances, A/C)...one of their "bigger" ones comes in a 2/2 configuration and is around $40,000.

Some folks I talk to are very much not into hearing about taxes, and for some sellers I was thinking of making a small, basic well-designed sheet that shows two or three ways of configuring the carry, with each one clearly showing the dollar savings at the bottom.

Talk to their tech support if you need help configuring.

I need my computer for me, and I would never let a connection like that into my network from the Internet for security reasons, and I don't have time to configure a VPN to lock it down.