Do you have to keep minions withing a group, within a certain range of one another?
If they remain within Short range of each other, do you require a PC to "Move" (Burn a Maneouvre), to engage another one? Of if they are Engaged with one of the group, are they engaged with the ENTIRE group? (Regardless of how spread out they are?)
Obviously, if the group splits to Medium range they would become 2 separate groups... but what do you think?
Minions aren't limited to being engaged, or even to being within short range of each other.
I've had minions groups where half the group is at long range from the other, and the whole group is flanking the PCs' party.
The reason you group minions is, IMO, twofold.
1) It provides a nice sponge for PC damage. The autofire PCs love them some stormtroopers 
2) Grouping the minions helps the PCs survive. If you have 20 minions within two groups of 10 each, they're doing way less damage to the PCs (on average) than if you were to have 20 minions in four groups of 5 each.
The "group skills" are really just a kicker. Unless your minions have terrible characteristics, they'll do way more damage (and be more survivable) ungrouped than they will be grouped.
Those are my considerations when I decide how to group my minions.
Do you have to keep minions withing a group, within a certain range of one another?
If they remain within Short range of each other, do you require a PC to "Move" (Burn a Maneouvre), to engage another one? Of if they are Engaged with one of the group, are they engaged with the ENTIRE group? (Regardless of how spread out they are?)
Obviously, if the group splits to Medium range they would become 2 separate groups... but what do you think?
There is no rule and honestly 10 guys in a squad strung out over Medium range in an open area is completely plausible.
I typically count them as a single entity for sanity sake. They are all engaged to each other, and can be engaged as a if they were one character. Otherwise you end up with the really weird issue of a Melee player attacking a Stormtrooper over on this side of the room, and killing one on the other side of the room. If they are so big I need to string them out, I break them up into smaller teams.