Just to add, you can get 600 ltr Ibc's if you are limited for space.
As for water production/storage,
Kent will be a high tds so water production quality will save you money,
Eg, if you use a Merlin ro, it will make water quite fast but will make high tds ro water, meaning it will use alot of Di resin, costing you money.
A 40/40 ro is expensive but better product water.
I petsonally use a booster pimped 450 gpd Ro-man ro, which is relatively slow, but produces really low ro water, which means i dont use a Di.
You also have to think of where you store your water,
Have you power/ water supply/ heating for the winter, insulated water pipes etc
Pumps to transfer water