I put my legion in a checkered like formation consisting of 9 legionnaires, 3 Legionnairy Cohorts, 3 Preatorian and 3 Urban Cohorts, 2 roman cavalry and 2 preatorian cavalry and 4 auxilliary archers i also have 1 general of course.

Pre marian, i have 3 trairii, 3 principes and 3 hastatii, again in a checkered formation, several velites in the front and cavalry on the flanks.

I use this in MP too sometimes when i play the romans.