I would be owner occupying, but obviously the ADU is not technically a "liveable" space.

In other words, just throwing money at it does not inherently add value to the property, you would have had to purchase it below-market-rate to be able to have the space to have the potential to add value.

I felt that had a lot of potential to not only update it, but to use the space better. 

Not sure if in Cali if you need to maintain office space, which is my main reason for not being a broker even though I have a brokers license. 

I would just continue to ask for the $750, not renew the lease in January, and start advertising the space early.

We have an offer in on a mixed use property with one retail space, one residential apartment above and two office spaces.

Unusual structure, originally a doctors house with living upstairs and the office practice space downstairs.  

We were thinking about using the apartments for like office space instead for the time being until this COVID blows over.

It's like comparing Disneyland park to your local theme park. 

If you're interested in learning about this space, you may want to start out with a few books on the subject.