It will probably maintain the value, but cash flow will not be good, probably not the best investment. 

I will start studying for the GMAT.

I have been studying for my boards recently and had to put my real estate ventures on the back burner for a bit.

Go through the education tab along the top and read through all the guides, read through starting out in RE under blog topics, and start listening to all of the podcasts.That will give you a good foundation and show you that there are different niches of real estate, and you will begin to think about your goals, and what you want to get out of real estate and then you'll be well on your way to studying the exact strategy you want to pursue so you can get into real estate.Until you decide what investing strategy / niche you want to get into, you'll be lost in the real estate sauce for a while.For instance...

I currently have nine units that I own and manage while maintaining a full-time job.

I figured the extra money through tenant rent and (eventually) investment would be very helpful with my lifelong goals. although I know there will be a challenge of fixing or maintaining the house would not be easy, I am up for the challenge. 

I hope it can be maintained. 

From the moment you decided to become a Landlord you  should have been consuming.Studying what area would make good rental areasChecking the market rents for that areaStudying expenses vs incomeStudying Vacancy Rates for the year You should have been consuming lots of time in educating yourself in regards to this business...Studying the Landlord/Tenant Laws of your stateAttending Landlord AssociationsAttending some Court Cases to see how the Judges view landlords and tenants, and the outcome.Studying the Permit laws of your State.  

I have a book deal and I'm writing over 30 case studies on different organization.

This is a well maintained multi with rents around $580 for a 1BR and $660 for a 2BR.