Should mention that Strelets' WW1 Russian Infantry In Winter Uniform is one of my favourite sets and will make good White Army opponents for your Reds. They are dressed in the ubiquitous greatcoat and "papakha" fur cap which was a combination frequently seen on all sides (Whites, Reds, Anarchists, Nationalists etc.).
For classic summer dress of peaked cap and gymnastiorka tunic you have a choice of WW1 Russian infantry from Strelets, HaT and Zvezda although they tend to look a bit too well equipped and "regular" for the RCW where supply problems mean units on all sides tended to look very "mix-and-match". Opposing sides often looked very similar (with the exception of those Red units equipped with the distinctive budenovka pointy hat) with the main distinguishing features being insignia - the Whites retained shoulder boards whereas their opponents did not.
In contrast to WW1, cavalry was able to make a big impression in the RCW so you might want to get your hands on some Strelets WW1 Cossacks (I actually prefer to convert Crimean War Cossacks as Kuban/Tereks wore a virtually identical uniform - just replace the muskets with WW1 rifles) for the Whites and Orion's Red Cavalry. Some Cossacks fought on foot so again converted Crimean War figures will work.
For field artillery you have the widely used Putilov 76.2mm gun set from HaT plus lots of French 75s, British 4.5 Howitzers and German Krupp 77mm guns found their way into all side's forces.
What we are chiefly missing are some Naval Infantry (who fought mainly against the Whites but started an uprising against the Bolsheviks at Kronstadt in 1921 as they felt the latter had betrayed the Proletarian Revolution!) and some decent partisans (Makhnovist, Grigoriev, Zelenyi etc) in varied peasant civies...