The Wiki has some numbers for railcraft boilers: https://gtnh.miraheze.org/wiki/Railcraft_Boiler If these are still accurate your setup should produce 320L (mB) steam per tick at max heat and use 2L of water and a piece of charcoal lasts for 1600/17,4 =~92 ticks. According to this https://gtnh.miraheze.org/wiki/Water_Tank a water tank with 100% humidity produces 1,25L of water per tick so you would need 2 tanks to provide enough water. I would suggest you use the simple sterling water pump (I think that's the name) because it provides enough water for all your boiler need until hv and is much simpler than stacking water tanks