About migrants, if you dont mind the performance hit of all those generated dwarves in your units list, just set up mass executions for the unwanted. That's what I do, and I celebrate when a blank slate peasant or single skill competent walks on the map. Create a burrow in a dug out room/constructed pen that can be locked by a single door. Name the burrow "Death Burrow" or something, and pick the red exclaimation mark over black for the look. Now, as they enter the map, you can assign them to the burrow, preventing any unwanted contact/friendships with your established citizenry. They will stall once you assign the burrow, and only one at a time will walk to your room, just be patient, and a few may run off for a bite to eat or a drink outside of burrow if they are staving/dehydrated. It's ok, it will be their last meal. Once they are all properly situated, just lock the door and forget about them for a while.
They will dehydrate before they starve. If you prefer starving them, make sure you dump some booze barrels in the room and keep them fobidden until you lock the door. Then you will get cool starving engravings.
A few years in, you can create faster methods with upright spikes, weapontrap sleeping areas, or just a retractable bridge over a deep pit or magma. If you can recover the clothing/tools, you can even sell them to a caravan. Immigrantite!
Immigration will slow naturally due to the massive amount of death, and you'll get cool messages of migrants braving their way regardless of the danger. You will need many memorial slabs, dont forget slabs are mason'ed and then engraved, no need for stonecrafting even at the craft workshop. One of my Slimers knocked off a child's arm, the kid survived splendedly.
Migrant waves are like reaching into that bag of scrabble tiles. You never know when the grand master weaponsmith is going to show up, don't let all the lye-makers and comedians get you down!