I'd like to use a construction loan, or have a second mortgage for a backyard cottage (DADU) but my current loan has a very good rate, and I wouldn't want to lose it.

In the past year I have been paying off some of the mortgages in lump sums due to the relatively higher interest rates and to not take up “golden ticket” slots with small mortgages ($50k mortgage with 5% interest for example).

Estimated at least 20-30 slots.... more if we clear out some of the lumber

I just moved out of Ventura County (Thousand Oaks), and I know at least where I was the city was very welcoming of ADUs and had passed an ordinance a couple years back that allowed many single family residences to have an ADU/DADU.

I can also recommend vendors to fill each slot that I have worked with and I respect each professionals expertise in each of their fields.

He says he will volunteer for any open slots if I don't cancel the lease. 

Tennyson Street/Berkeley is an awesome location in Denver, but those slot homes are pretty tiny, and you're right -- no storage, no parking.

Proof of how many slots were rented for what length of time.

If the potential partner can't be slotted into one of these 3 reasons to be a partner, then DON'T have them as a partner:1 - Do what you can't do2 - Do what you don't want to do3 - Do what you shouldn't do.

Just my quick 2 cents on this, I would say the following might be some: Flexibility of termsNo credit impact (don't use one of your Fannie/Freddy slots either)Ability to quickly negotiate and adjust if something comes up where you can't payI'm sure there are more, but those are just a few