Obviously, you know the exact details of your situation.  

I haven’t looked at the details of it yet. 

There are small details along the way that are important to understand and are too easy to miss while researching on the internet.

The best thing to do is get as much detail as possible from zoning restrictions to what can actually be built on your combined properties, then get some numbers together to see if it makes sense, as well as get your neighbors lots under contract.

Is it rocket science, well no, but the average homeowner/seller is also clueless on those items.

If everybody showed up, I would be there to answer any questions, and serious tenants would stick around until the end asking more detailed questions and taking applications.

I will try to be brief but detail. 

I will however take your recommendation and research other multi units in the area to detail market rates.

Since it is a condo, you won't have to worry about exterior items, but self-managing low-end tenants can be a challenge and with 21 units you won't be able to afford decent management.  

I would need more details on the Property, the style you are trying to accompLish, and the numbers on the project to give you the most accurate answer.