Don't choose a RE genre right now, the houses will dictate what you do.

I've included a preliminary floorplan below.My goal with this ADU is flexibility in terms of renting it out either short-, medium- or long-term rental in the future for income, as well as maximizing resale value (main property is 1300 sq ft 3/2) to someone probably with an investor mindset who would want to house hack.My main concern is whether it's a good idea to have 3 en-suites at the expense of having a small living room/kitchen area.

And it's unlikely they can afford market rates after the renovation.Give them plenty of notice and be flexible if they find something early.

You will probably have a little more price flexibility if you're looking to hold and rent the home, as rehab costs will be considerably lower on a rental as opposed to a retail (flip).

In my experience, the banks have been flexible in moving the payment dates around for my clients.

This approach provided the flexibility needed to address unexpected challenges, such as the foundation issue we encountered, without delays.

This approach provided the flexibility needed to address unexpected challenges, such as the foundation issue we encountered, without delays.

But if you are simply a group of friends/acquaintances buying a property as tenants in common then it's pretty straightforward and flexible. 

Gives you flexibility + exposure within a small community.

A flexible closing date is a good idea.Your earnest money could also make you stand out.