Overall a cool idea but did come up with a few points...
*I think the size of some bands/ gangs would vary from 2 or 3 members up to 25+ depending upon whether they are organised or opportunistic. I could see the small opportunistic raiders groups as friends or family that are looking to make a fast buck. While larger organisations could hire themselves out to rival merchants. Just like the Yakuza gangs perhaps some larger "crime families" could have existed since the dawn of the Empire; groups who refused or reluctantly embraced the new Empire but continued with their own codes of conduct & motives. Some raider gangs could even be sponsored by the clans to raid their neighbours and competitors.
*I like the idea that some bands might set themselves up in long abandoned Devanu towers.
*With the Tower there would need to be a reason why they themselves have not been broken up by the knights. Perhaps they are to organisations in one ala the IRA (raiders) and Sin-feign (public face of mercenary/ trader organisation). The location of their base would then likely be a rumour as such underground groups would be unlikely to last long if its location is known.
Just a few ideas.
HN