I am slowly building up parts of the next stage of the car's development.

I have been able to source some brakes, but probably won't be put on a few months if not 1 year.

What is the best way to store them, so they don't corrode? should I fill them with anything? or just flush them with brake cleaner/water, coat in light oil and leave?

if they are second hand (been used) leave the brake fluid in them, if they are new dont fill them with any thing!
a spray of oil/ silicone lube wont go amiss, watch the rubbers cos mineral oil will destroy them. another thing that will perish the rubbers is sun light, so try keep em in the shade!
i'd be tempted to make a plug to fit the brake pipe hole to stop and dust bits n bobs getting in there!