DWC bucket size for flower and veg

Hey guys,

Changing from dirt to hidro and running a 60x60x120 cm space with 250w hps cooltube.

I want to do 1 plant scrog with DWC.

My doubt is about the container size, i'm thinking:

Veg - 100w cfl - 10 liter container = 5 liter water/solution

Flower - 250w hps - 15 liter container = 10 liter water/solution

Is this enough or is better to go with 5 gallon = 20 liter ?

Thanks.

The buckets i saw look like this: