Just another opinion FWIW:
- Since you live in the bay area, a common trip is to drive up to Lake Tahoe and other regional mountainous areas.
- Since you are buying it as a family hauler / work vehicle and not for conversion use, there is a good chance that you will end up pulling a trailer or boat over the next 5 years. I say this just because I have raised 4 children and have grand children.
- Gasoline will have fewer issues in cold weather (snow related trips) than diesel
IMHO, that means that you want a van with a lot of pulling power = ecoboost.
Just so you know, the ability to order a custom feature on a Transit appears to be almost as challenging as sprinter, so make a shockingly detailed feature list of what you absolutely want vs could add yourself or do without. Probably you will end up buying something that exists if you want it in the next 90 days.
I know that you are saying that you want a low roof version, but those might not be as easy to find as you think since the market is heavily buying high roofs.