Hey, I have not read all replies but I hope my advice can help anyway.
When I was still new to the game not knowing how to manage all those dwarves, something I did was start a fortress with the single purpose of trying out every single workshop and task.
This gives you an idea what sort of industrial processes require what kind of materials, how much labor and what kind of results are yielded, giving one a very clear grasp on what dwarves could be doing.
Armed with that knowledge I was much more able to plan ahead for migrants, often not cursing a wave of migrants but being relieved I could get to the next step of the plan to industrial dominance.
Metalsmithing especially is something I attribute many dwarves to early in the fortress, up to 4 smelters and 2 smithys for whatever purpose together with a good 20 haulers to supply it all.
A second bit of advice from me is not to hesitate to long about a military, especially if you've thouroughly figured out the metalsmithing industry and you're churning out weapons and armor. The sooner they start training and gearing up the easier the first ambushes will be to deal with, wich leads to your military being experienced wich makes everything so much more easier.
If you've still got idlers about mass dumping is not a bad idea, if only for the sake of tidyness.
But really, try it out make a fortress and just set up as many workshops as possible and try out producing every item ingame. It really helped me back when I was starting out.
Oh I forgot, I have never used dwarf therapist and have gotten used to micro managing jobs. I make it my habit to go through every migrant, and assigning them a single useful labor or keeping them as generic haulers I may or may not pick out for some other workshop job. Also custom profession names can help you keep track. I guess I have a good enough memory in this case, I have no problem remembering the labors I painstakingy assigned each and every dwarf.