I have never been there so I can't say for certain but wasn't Marzahn basically our version of Ballymun-a large area of soviet era flat blocks built outside the traditional city boundary by the DDR government?
I'd never write anywhere off-people have made money in unlikely places but from my reading Marzahn is not overly positive. I'd pick a more 'run down' spot but closer to the city centre maybe, with better transport links (the DDR couldn't afford to expand the U-Bahn and instead expanded the tram network). I don't think it'll be all that easy to find tenants tbh.
You give away your location with the z instead of the y btw, lol!
Disclaimer: I recently bought in Neukoelln, another "working class" area of Berlin which used to be in the west, near the wall with Treptow in the east. Best of luck in whatever you decide and good luck.