Please make the ukranian faction unless you are going to incorperate ukranians on the russian team.
Ukraine was part of the Russian Empire in that time, not an independent nation.
The Cossack Hetmanate was autonomous well into the 1760's, and did have it's own independent army; Ukrainians fought on both sides of the war. There were Mazepa's Cossacks (What I would consider true freedom-fighting "Ukrainians"), who fought under Karl's banner, and those Cossacks who stayed subordinate to the Russians (Being most of them).
As I've stated before, I'd love to see Ukrainian units embedded in both factions, but certainly not as their own independent army. I'm rather of the position that Mazepa was a hero to Ukraine, and I think most Western Ukrainians would agree. Eastern Ukrainians, of course, would be more opposed to that thought, I should think. Thus, I think it would be fair to simply include them in both factions, with varying equipment and uniforms as an auxiliary unit.