I think there's probably a good amount on each side, the Imperials and the Rebellion. Probably numbering in the tens of thousands. But for the purpose of the RP, the main focus should be on Childebrand's Fighting Group and the Chasseurs. I guess my view of how the Panchalans were set up was along the lines of the Australian Imperial Force, where they had a lot (like, 70 or so) battalions organized into their force. The whole organization of the Imperial Army is based around the planetary regiments, which are sort of home-units for the battalions which are (typically) leased off into ad-hoc operations under generals. With the Civil War, the principal organization is the Sector Divisions, since the war has grown in such scale. But in the tactical situation, the ad-hoc formations still reign since the doctrine trained into the general staff is hard to break.

My view is that the Panchalans represent just a sliver of the fighting force on the planet, perhaps on a few battalions of them (We could say, the 13th, 17th, and 21st Battalions). The rest are from the Volksgrenadiers, which we can say are the post-outbreak of War units raised to supplement the regimental system, and specialized armor, artillery, and air support units. The Volksgrenadier Regiments are attached to the Sector Divisions in which they were raised and are smaller than the planetary regiments, resembling more of what you would know as the typical regimental battalion size.

The Opposition Forces, I think, should be Alpha Centaurian since we are going with the French theme. My belief on them is that they adapted to a numbered regimental scheme more than the Imperials since they would've had to raise a large amount of men in a quick amount of time, and not many of the Imperial Army regiments would've defected. But we can have some of the units be defectors, say like the 20th, 33rd, and 56th Battalions of the Régiment de Centauri populaire (formerly the Régiment royal de Centauri, renamed to fit the Communistic-like fervor) and some battalions of the Centaurien Chasseurs, with some armor, artillery, and air support units. We can also have some Régiment révolutionnaire (Revolutionary Regiment) units, which will be the same sort as the Imperial Volksgrenadiers.