The elven ambassador keeps insisting I limit my wood harvesting to just over 100 trees per year. This is highly disruptive to my alcohol industry, as I require wood to make barrels for my brew. What happens if I disregard his requests and put my woodcutters in high gear?
Depends. Sometimes the elves will notice and take action, and other times they will ignore it.
If they do notice, it is also possible that the worst that can happen is that they leave as soon as they arrive. In a worst-case scenario, I think they can be provoked into outright fighting you. (Not sure if that counts as a war / siege)
Don't forget you can also build barrels out of metal if you are in a biome with plenty of ore. In some biomes, metal is as close to infinite as you're likely to need when you consider how many z-levels down the map goes. Fuel may be less infinite, so magma becomes important quickly!
Two other advantages: metal barrels sell for more (and elves will buy them), and the metal industry employs more dwarves than the wood industry so you can support a larger population.
Make stone pots to store your beer!
Wood: If you are trying to avoid annoying the elves, save your wood for items that can only be made out of wood. Beds and training weapons are the only items I am aware of that require wood. If you DO want to annoy the elves, clear-cut everything, and then attempt to sell them the wood when they come to trade.
Metal: Although you can make barrels out of metal, this is not the optimal use for metal; metal is better used for weapons, armor, and coins.
Stone: The best thing to store your booze in are rocks! It's more dwarfish and you have a never-ending source of them, assuming you are not blocked from deep mining by an aquifer (stupid aquifers). The 'large pot' container type can be made out of wood, stone, clay, glass, or metal. Pots hold as much or more booze than barrels (depending on DF version*), but weigh 1/4 as much (for any given material type), allowing your dwarves to move them around faster.
Making a stone pot requires one stone at a craftsdwarfs workshop.
Making a glass pot requires one glass at a glass furnace (making glass requires sand and a bag at the same glass furnace)
Making a clay pot requires one clay at a kiln. If the clay is silty clay, sandy clay, or clay loam you will need to glaze the pot afterward to store booze (or any liquid), but fire clay or kaolinite do not require glazing.
The DF wiki on containers is here: http://dwarffortresswiki.org/index.php/DF2014:Container
*Note that the pot against barrel size comparison alters depending on your version of DF. In earlier versions (version 0.34) barrels held 3000 liquid. Now (version 2014) they hold 6000 liquid. Pots have always held 6000 liquid.