Thanks in advance A joint venture partnership is a partnership between two or more people who want to combine forces to attain a common goal.

No common areas that use water.

Go with the most commonly occurring (the mode)?

very common strategy for high net worth investors..  

Expecting to get a quote that you are looking for by just showing the pictures to the contractor is not going to work .Even if someone agrees once they start work they will bring up or scare you with other things inside the house and the common excuse will be that they never saw the house.

Also, the project could actually take longer than the 1st house if the contractor adds contingency days to the schedule to mitigate the risk of damages  Good luckAs far as the payments go, there are 2 standard billing practices, percentage of completion which is by far the most common or you include drawers in the construction schedule based on completion on milestones.

I believe most (I do not really know the stats, but fixed rate is an common option) refinances are fixed rate.We use HELOC for shorter debt such as to purchase a property that we plan to value add and refinance in the near future. 

Or do you get a mortgage that is split up as a tenancy in common or joint tenancy?

In my state, this is the most common way to transfer ownership.

In Worcester they have what is called ZERO LOT LINE where you can share common walls with someone but everyone is responsible for their own exterior maintenance and roofs.