Just some information about the size of regiments and such (only combatants in the Great War):

Dornish Armed Forces:
Infantry regiment: 2,100 men, divided into ten companies of 210 men designated A-K, in turn divided into 7 platoons of 30 men designated A-G
Cavalry regiment: 1,500 men, divided into ten companies of 150 men designated A-K, in turn divided into 5 platoons of 30 men designated A-E
Weapons used:
Infantry, Oldtown 15 rifle
Cavalry, Lysene Cavalry Carbine 7 (LCC 7)
Dragoons, Myrish Dragoon Carbine 3 (MDC 3)

Reachman Armed Forces:
Infantry regiment: 3,000 men, divided into fifteen companies of 200 men designated A-P, in turn divided into 10 platoons of 20 men, designated A-K
Cavalry regiment, 2,000 men , divided into ten companies of 200 men designated A-K, in turn divided into 10 platoons of 20 men designated A-K
Weapons used:
Infantry, Oldtown 15 rifle
Cavalry, Oldtown Horseman's Rifle 1 (OHR 1)
Dragoons, Oldtown Dragoon Carbine 8 (ODC 8)

Westerlands Armed Forces:
Infantry regiment: 2,500 men, divided into ten companies of 250 men designated 1st-10th, in turn divided into 10 platoons of 25 men designated 1st-10th
Cavalry regiment: 1,800 men, divided into ten companies of 180 men designated 1st-10th, in turn divided into ten platoons of 18 men designated 1st-10th
Weapons used:
Infantry, Lannisport Repeater 4 (LR 4)
Cavalry, Swyft Cavalry Rifle (SCR)
Dragoons, Lannisport Dragoon Carbine 11 (LDC 11)

Riverlands Armed Forces:
Infantry regiment: 2,000 men, divided into ten companies of 200 men designated 1st-10th, in turn divided into 10 platoons of 20 men designated 1st-10th
Cavalry regiment: 1,500 men, divided into ten companies of 150 men designated 1st-10th in turn divided into 10 platoons of 15 men designated 1st-10th
Weapons used:
Infantry, Lannisport Repeater 4 (LR 4)
Cavalry, Swyft Cavalry Rifle (SCR)
Dragoons, Lannisport Dragoon Carbine 11 (LDC 11)

Valeman Armed Forces:
Infantry regiment: 2,100 men, divided into ten companies of 210 men designated 1st-10th, in turn divided into 7 platoons of 30 men designated 1st-7th
Cavalry regiment: 1,000 men, divided into ten companies of 100 men designated 1st-10th, in turn divided into 10 platoons of 10 men designated 1st-10th
Weapons used:
Infantry, Lannisport Repeater 4 (LR 4)
Cavalry, Swyft Cavalry Rifle (SCR)
Dragoons, Lannisport Dragoon Carbine 11 (LDC 11)