The first migrant load is usually a 'okay, now what am I REALLY doing in this fort' kind of moment. I can tell you what I usually do.
My opening moves are survival and defenses, so my founders revolve around that. Farmer and Hunter make two. Two miners, to get down into the earth faster, that's 4. Carpenter for beds/tools/tables, Mason for walls, and Woodcutter to feed the carpenter round off the last 3. That doesn't leave me a lot of mobility. That first huge migrant wave becomes a lifesaver to fill in the gaps.
Typically, a few more migrants get tossed into masonry for walls. One or two get thrown at crafting the thousand or so bones I've collected for the first trade caravan, and to start making a large collection of bone bolts. A dedicated brewer (or 3) and cook (or 2) get tossed in the mix. A few more join the farming legion and I get all crops going, including surface crops. Next up is clothes. Plant Processor for the rope reed/pigtails, Spinner/Weaver for threads, and 2 clothesmakers to start making replacements. Leatherworker doesn't hurt to start training now either, because you'll need a decent amount of armor eventually for your marksdwarves unless you're fitting them in metal as well, but that's probably a long ways off. Either way quivers are a must, and backpacks and waterskins are helpful. A few more miners to start digging out the apartment complex, and a bowyer to start mass production of crossbows.
Anyone left with marksman capabilities gets thrown in the military as a marksdwarf (or perhaps hunter, depends on how populous the local environment is). I usually have an emergency squad for the hunters to be pressed into military service on a moments notice. The rest become haulers. By the time that wave gets there usually there's a few metric tons of wood, stone, and food to be hauled. Swap your haulers out of 'hauling' and into whatever jobs you may need as you go. Milller for dyes? Check, Urist McWhosthat gets pressed into service. Also start watching for people who will be good in the hospital staff, you'll need them shortly...
... at 80 dwarves is when the sieges will start to come play.