If you are going for multi-figure basing, I use 1" x 1" bases with 3 figures to a base for natives. For Europeans, I use 3 figures abreast on a 1/2" x 1 1/2" base. Cavalry either 1 1/2' x 1 1/2" for natives or 1" by 1 1/2" for Europeans. Artillery to fit - though best to base the crew separate, I use 4 figures with two to a base, 1/2" x 1".
If you prefer single figure basing, I'd go with round steel bases (they can be purchased in bags of 250 here in the US), 3/4" for foot, 1" for mounted (that is what I am doing with my Very Large Skirmish Three Musketeers).
Hope that helps.