Hi Mick,

Yes, the 50mm X 25mm bases are used for cavaly.  The bigger 50mm X 50mm bases are used for elephants & artillery units.  I usually base my cavalry with three horses per base.  Some use 4 per base, but I think it looks too crowded.  For light cav, I only put two horses per base.  It really doesn't matter how many figures you use per base as values are calculated per base.  Hope this helps.  Good luck and happy gaming.