Elf Game and Theory: Military and Defense
Elven military forces, in their flimsy wooden armor and armed with equally flimsy wooden weapons, need to be as skilled as they can to survive against goblin ambushes. Bringing along enough armor and weapons for two of your starting seven and sending them straight into the military can help keep you safe in the long run. Such wooden equipment is dirt cheap, so it doesn't make a major impact into your resources, though it also lacks the quality modifiers later pieces of equipment brought by traders might have. Don't buy shields at the embarking screen. Have your carpenter make them instead, so that they can at least get some minor benefit from a quality modifier.
Whatever you do, do NOT give your military any weapons until they've managed to put many, many levels in wrestling and shield use under their belt. This is an almost universal truth in Dwarf Fortress, but it goes doubly so for elves. While wooden weapons don't do terribly much damage, it has to be remembered that wooden armor doesn't stop much damage either. Kitting your early military out with wooden swords will result in a non-stop string of bruised heads, necks, and spines that will prevent them from ever training again and may even leave them bed ridden. You absolutely cannot afford this, because you'll need every last soldier when the ambushes begin.
A uniquely useful option for elves, one which works far better with them than any other race, is to create a 'civilian milita' out of your non-military elves. By crafting enough bows and arrows and importing enough quivers, you can take advantage of the Hunter profession to give every last member of your retreat a weapon. Your so-called elven hunters will never actually do any hunting (unless you are on an evil biome or an area with an open pit/chasm, in which case do NOT do this unless you want to have them all die in battle against werewolves, skeletal elk, or antman swarms), because elves would never harm such cute furry animals.
They will, however, happily turn those bows on every thief, ambush or siege that shows up. Lacking in skill as they are without the practice from hunting and weak as wooden arrows tend to be, the sheer volume of arrows they are capable of putting out is often more then enough to make up for that.
One of the biggest potential threats to your retreat, even on a good or neutral biome, doesn't actually come from goblins, but from the same cute furry creatures your hunters won't hunt. Animals prone to thievery, such as raccoons or rhesus macaque can be a bane upon your retreat like no other. There is simply no way to really stop them. Your elves will ignore them as they run in and make off with tons of masterwork cloth or clothing or, in the early game, just leave you near starvation by stealing all your food. Creating warehouses with doors can slow them, but it won't stop them. The plundering little thieves just line up outside the door, waiting for the moment you need to open the door to retrieve goods for production or trade, when they will rush in and swipe whatever they can.
As truly elfy elves, you have only two real ways of stopping them. By keeping all of your most valuable goods locked away somewhere and deliberately leaving some cheap, low value items out in the open, you can at least attempt to trick the thieving bastards into only making off with products you're not worried about losing. This will still cost you on fortress value, but it does at least help prevent seeing your master clothier go insane because monkeys stole the six dozen masterwork socks he had made. It does require some vigilance though, as you'll likely need to keep the warehouse door unlocked so your elves can get in and out and so must lock it quickly whenever the thieves enter onto the map.
The second option is somewhat less elfy, but also better for the retreat and requires you to do a little light mining. You'll need some stone, you see, in order to make mechanisms for cage traps. By trapping in or around a warehouse area, you can transform the annoying little buggers from hazards to pets and trade goods. You could also theoretically accomplish this by creating a smelter reaction that allows you to transform wood into mechanisms. Either way works and, hey, don't feel too bad about it. The elves have to get those pets they trade you somehow right?