Belt-driven wheels (not direct-drive; this is to isolate the motors from impact force on wheels from, e.g., another spinner or from fall/toss damage)
Slip-belt-driven spinner (slip helps protect the weapon motor from stalling and burning out)
Milled armor; each piece must be within an 11"x4.5" millable area due to the limitations of the milling machine I'll be using.
Minimize in-shop time. (I have a 4-month old, so I have very little time for construction right now. Design for CNC milling on fabricated parts and off-the-shelf parts wherever possible.)
Power switch (I always forget this one until the last minute!)
Field-serviceable:
ability to quickly swap battery (or at least have easy access for in-place charging)
wheels and belts easily replaced if damaged/destroyed
If time and weight allows, allow easy swapping of weapon blade for a saw blade.