I suppose it depends on what unit size you are using. When we played a lot of Hail Caesar with 10mm figures, based for warmaster on 40x20mm bases, we used 6 bases to make a unit with a foot print of 120x40mm. It was a bit fiddly to move around, so I would probably use 40x40mm base now, with 3 to make a unit. If you want a more linear look then going for 40x30mm bases would work too.
With 3 bases per unit should be easy enough to move around, and can be re-arranged into column easily enough. Square will be a bit untidy...
Sabot bases are also a very good approach to let you use smaller bases to give flexibility for other rules, while making manoeuvre easy.