Here's how to maximze barrel capacity. Create five food stockpiles.
1) Prepared meals only. No Barrels
2) Seeds only. No Barrels (need bags)
3) Drinks only Need Barrels - keep this one near your brewer but away from most of your dwarves.
4) Plants only Need Barrels
5) "Have a drink stockpile". Smaller 2x2 or 2x3. Very centrally located, takes from the drink stockpile, uses barrels.
1) Prepared meals don't need barrels as they will never rot when inside.
2) Seeds do not need barrels only bags
3) Keeping your main drink stockpile far away from your dwarves will deter them from "booze grazing" where they just sip evenly different barrels, causing tons of half-full barrels.
4) Plants need barrels because they will rot faster without them. BREW YOUR PLANTS AS SOON AS POSSIBLE to give them longer shelf life.
5) Having one central drink stockpile of 4-6 barrels will cause dwarves to drink barrels until they are empty, freeing them up for your later use.
Other barrel saving tips
* Allow food to be mixed in the options. This will save barrels in your plant stockpile
* Only cook booze. This will free up barrels and create perma-meals that will never rot and don't need barrels. If you're good on barrels, you can cook seeds instead.
* Buy all booze and barrels sold by merchants. Every barrel of booze you buy is a barrel you don't have to make yourself.