My general process for handling migrants' labors is to assign them immediately when the migrants arrive, and nickname the dwarf or give them a custom profession title to signify that they've processed. Yes, that does mean I go and check their skills one-by-one and then assign appropriate labors, but you only have to do it once per dwarf. I try to strike a balance between what the dwarf is good at vs. what I need, but don't sweat it too much if my needs are covered.
What Shonai_Dweller said is very true though. You really don't have to worry about being on top of every single dwarf's labors once you've got a few dozen. I just try to get 2-3 dwarves per job, more for important industries, and let them go. If some end up working suboptimally, that's fine with me.
For the starting seven, I usually go with something like this:
1 militia dwarf with a bronze weapon and helmet, maybe a breastplate if I really splurge. I put 3 points in the relevant weapon skill, then spread the remaining points out over dodge, armor user, teaching and leadership. The last two supposedly help with training new squads, but I'm not sure how true that is or how much it matters. Don't bother with fighter since it trains up fast on its own.
1 medical dwarf with 3-4 points in diagnosis and 1-2 points in plant gathering. Enable all medical labors once you embark.
1 wood cutter, no skills since they get that fast when cutting trees.
1 miner, no skills since they get it fast and easily.
1 cook, 1-2 points in brewing sometimes, sometimes with nothing since they're fast and easy to train up. I enable cooking and brewing on this dwarf until I get migrants to help with the load.
1 dwarf with maybe 3 levels of carpentry and masonry, who serves both roles. I usually enable carpentry, masonry, woodcrafting and stonecrafting on this dwarf until I get migrants to help out.
1 farmer with 5 levels or so in growing. Enable all farming labors once you embark.