Here is almost all the knowledge you need to create the Red Army, some of it might not trsnafer well in HOI2, but you can use the info you need, some of the units are probably not easy to represent in HoI2.
well as for the Reds its hard to say, but by April 1918 there were at least 155-200,000 men in the Red army. The Bolsheviks idea was to create a total of 58 Infantry Divisions and other specialsts and technical troops.
As for Fronts here they are (they are highre than an army) these would be HQ's in my idea
Northern Front - Volodga-Archangel area
Ukrainian Front - Ukraine
Southern Front - Ukraine to Azov
Turkestan Front - Turkestan
Caspian-Caucasian Front - Caspian region and the Caucasus
Eastern Front - Urals and Siberia
Infantry
Army/Field Army (Armiya)
A Field Army consisted of around 2 to 9 Infantry Divisions this was around 12,000 to 50,000 men
Infantry Units:
In 1918 all Infantry Divisions fighting for the Red Army were designated as Rifle Divisions, or Strelkovy Diviziya. It had 1,657 Officers, 56,668 Other ranks, 382 Machine Guns and 116 Artillery peices, but most Divisons were of around 15,000 men instead.
Cavalry
Cavalry Armies:
At the time in 1918 there were only a few Cavalry armies. There were 3 Cavalry Armies: the 1st, 2nd and 3rd Cavalry Armies.
Cavalry Divisions:
A Red Army Cavalry Division comprised of 3 Cavalry Brigades and 4 Horse Batteries. Full strength should have been around 9,499 men and 10,210 horses. In practise it was usually between 3,000 and 8,000 men
Specialist Forces
Air Forces:
The Red Army airforce in early 1918 consisted of around 113 men with 6 planes.
Armour:
There were armopured car detachments but they were foten very small. In 1920 the Red Army set up the first Avtotankovy Otryads or Auto-Tank detcahments, they had around 81 to 113 men. Most of their armour was captured from the Whites and therefore of Allied make, the majority were British with some rare French vehicles appearing here and there.
Paramilitary security forces:
The Voyenizirovannaya Okhrana or VOkhr was formed in late 1919, their job was to gaurd roads, factories, bridges, waterways and railways that were strategic. By early 1920 there were 105,000 men in the VOkhr.
Internal Service Troops:
The Voyska Vnutrenny Sluzhi or VnuS were created in early 1920. Their responsiblities were to gaurd POW camps, communictaion networks, and to convoy anti-Bolshevic elements to their POW camps.
Border Guards:
The Pogranichniye Voyska were established in May 1918 to defend the Bolshevik borders from attacks from whites etc. But it they never really did their job properly till the wars had finished and the Soviet borders were re-instated.
Specialist Equipment:
Aircraft:
The Reds used many planes, 2 thirds were foreign made. 50 percent were French Nieuport fighters and French Farman Bombers. Russian made fighters were rare, but still served. They were the Ilya Muromets and the Lebed-12 Fighter and the C-20 fighter plane.
Armour:
The majority were British Mk.I and French Renault FT-17's but they were only avaible when captured from the Whites.
Hope this info is helpfull to you.