Okay, i made it to year 4, even with tons of Ogres etc. attacking. Here's how i managed for those that are struggling:
For embarking, take whatever you want but
at least one Crossbowman. Give him Ambusher so he starts out with basic Equipment and Ammo. I highly recommend taking some extra Ammo, especially if you take multiple Crossbowmen.
First of all, secure your Fortress Entrance. I repeat, that's the FIRST priority if you don't want to get killed. Depending on where your entrance is, dug into the side of a mountain or just Stairs into the Ground, pull a Wall around it that can only be accessed with a Drawbridge (Link it up fast so you can close it off). Carve Fortification's into the Section and build a Floor above it if necessary, (if you want to avoid that step, make the Draw bridge a bit deeper into the Fort, so there's allready a Ceiling, keep in mind tough, the farther in, the farther all Migrants will have to travel to get in safely.). Then carve Fortifications into the Wall and make a Burrow at the Location. Make a Ammo Stockpile nearby so the Guys don't run out.
Now, if those pesky Enemys enter your Land (i'm not talking about Ambushes and Sieges, just those random-Visitors like Ogres. Tough the Trick works for the first few attacks.) pull everyone inside, a second burrow for Civilians works nicely, and let the Enemy approach your Entrance, then seal of the Drawbridge if he gets to close. Of course, draft your Military to the Burrow you made so they start shooting. Should he go too far away for your Crossbowmen to shoo them, open the Bridge again. Repeat as necessary.
As soon as your Basic Fort is established, you can add a second Drawbridge a bit further away from the other one. If someone enters the Area, close both Bridges, leaving the Guy trapped between two Walls and your Dudes shooting at him. Remember to add more People to your Military over time, especially trained Meele's. Later Ambushes and Sieges get very hard, especially with all Races enabled. If you don't want to be trapped in your Fort forever, you need a Method to kill things, BIG things. But this should get you trough the early-stage, at least for me it worked