I've been slowly making a Marian/Caesarian legion. So far I have 10 cohorts each with 10 figures on a 120 x 60mm base. I decided on a tribune and a primus pilus for the the sub commanders. I have Balearic slingers ready to go as well as some javelins and a pair of scorpio's on the way. I'll also need a few cavalry figures and a general (I atually have a Warlords general but the figure is crap).
I really like the base size which, as you may have guessed is right for Impetus. However, I doubt that I'll use them with those rules. I just think that the base size is right.
I also have another hundred odd figures ready to make a second legion but that can wait for the time being.