What are the must-have features for a Hackspace/Makerspace horizontal metal bandsaw?
From my perspective, I cut lots of metal and cant live without my horizontal bandsaw, I cant tell you what is must-have, but I can tell you the features I like. 


Auto off switch at the end of the cut (sometimes cutting large sections you dont want to sit at the saw. 
Clampable vice which firmly holds the metal, and is degree adjustable BUT with quick release/adjustment coupler so you dont sit there winding the clamp to get the desired with.
Bin for cutting fluid should you buy the attachment to spray cutting fluid onto the blade.
A common blade size which is cheap and readily accessible
Hydraulic assisted arm which you can adjust the effective "weight" so that you can set the machine to apply a constant pressure to the cut. 
An additional feature is a vice with 2 degrees of angle, (up down, Left right) - this will enable compound mitre cuts. 
E-Stop, for when the blade snaps


Hope this helps