There are No Official base sizes for saga, so run what you got is fine.
The "official" line of figures (gripping beast) are supplied with 25mm rounds for infantry, 50mm x 25mm for cavalry(I believe, not 100% on size of this one), and a 40mm round for the warlord. (all renedra flats in the "official" packs)
The party line is common sense should rule, over madness.
The easiest way to think of it in game (how me and my friends cover it) is that Infantry will fight 3 deep when touching, and Cavalry will fight two deep when touching. That will cover most variances due to base sizes, and avoid unneccasary measuring and fretting.
I suspect it should only be a problem in tournements, where upon the organisers should take this into account any way, and produce a tournement ettiquette for this and how they are handling it.
Other than that, get the rules, a brilliant game.