Hackberry

I was very late to a recent native plant swap and by the time I got there there was not much left of the 5,000 seedlings and small plants they had started with.  The currents I wanted were long gone but there were still a handful of few seedings left in the shrub and tree area. They were trying to empty the tables as it was the very end of the swap and as a result I ended up with 2 tiny Hackberry seedlings.  One they said for sure is a Celtis occidentalis but they said the other didn't look right for that species and may be a Celtis reticulata.

So far so good except I am like umm what the heck  is a Hackberry?  How big do they grow and is there any way to keep one small enough to fit on a tiny city lot?  
I have gathered that they have small berries that are edible and of course that the birds like them.   My 2 seedlings are tiny  just started seedlings so I will have some time before I will have to find a permeant place for them but it would be nice to know what size space I need to look for.

My property where our daughter lives has a row of hackberry trees along the property line.  

I am not good with distance though I am guessing they are 25 ft tall.

Coppicing would work to keep them shorter:

https://permies.com/t/116394/woodland/coppicing-Quick-intro