its not Big Mom is at the same time an empress like Cobra or Riku she has her own royal army like other large nations but those 10.000 are nothing compared to the 30.000 on onigashima island
she has prob many hundered thousands of fodder soldiers and prob a crew big as the other emperors
Oven Alone has 10000+ Soldier they Also send 10000+ for Germa
3 Big Fleet With 100+ Ship Was After SHP
Big mom main Fleet and Sheep also Appear in End of Arc and it has many Sheep
10000 of 30000 are For Orochi also many of Kaido's Soldier in normal condition are in they're Position (Many in Prison Mine and other Factorys some in Charge of Town's Like Holdem)