Crimean War Cossacks Question

[OB]

I have three units of Crimean War Cossacks to paint and base.

My initial inclination was to base them as regular light cavalry.  Then it occurred to me that not all Cossacks might be regular cavalry.  Some might operate as irregular cavalry.  Tribal cavalry if you like.

I'd be interested to hear how other Crimean War gamers rate their Cossacks.