I played lucius in a league for awhile and after about 2 weeks of getting my teeth kicked in I started getting smart with him. He is great with schemes and strategies that want lots of scheme markers, but with the right crew he can do some work... or his minions can do work.
I almost always take a doppleganger because if ill omens with him, plus she is a great scheme runner and even proxy beater depending on the situation. If the schemes and strats are more killy consider throwing in some changelings because they can copy attacks (at MI/Sh/Ca 4) which is additional stuff. It doesn't sound that good until you consider putting them next to a hunter or peacekeeper who has a 10" slow they can just fire off (and and Sh 4 who cares about cover, just volume of attacks things).
Within guild, I think riflemen are a trap, but austringers are always amazing, put one in every crew. Since you already have Sonnia, Witchling thralls would be great whenever the come out. Those models pair well with Lucius due to automatically passing horror duels (i.e. free AP even on black jokers) and Sonnia (an impossible to wound beater in your face with disrupt magic giving masters negatives to cast). He also likes Santiago as a soul stone battery who he can punch, which there is a previous post on. And any beater model, judge, ryle, phiona etc, is never a bad choice for him.