I'm eleven years into a 200 dwarf fort. I've spent over sixty hours the last few weeks playing it. I started off by reading each and every migrants' thoughts and preferences, making notes, sorting out family relations, etc. After the first sixty I stopped because it was just taking too long. I had a migrant wave of thirty dwarves once and it took me more than two hours to go through them all.
I've found Dwarf Therapist really useful lately. I want to add another scribe to the library. Dwarf Therapist > Other Skills > Sort by Writing Skill. Bam! The five dwarves out of 200 that have any writing ability are at the top. I have three military squads but I want to form a fourth one. Dwarf Therapist > Military > Sort by Armor User, Strength, Discipline, etc. A big one lately is sorting by happiness. It is quite helpful to know which dwarves need some TLC to keep them from going over the edge. If they haven't seen friends or family I unassign all their hauling labors with a single click, which usually takes care of that. Some dwarves don't know when to take a break.
When the caravan arrives sort the dwarves by number of skill levels assigned. The ones without a lot of responsibilities get assigned trade goods hauling so my craftsdwarves can keep going with whatever they're working on. I can assign all the hunters to hunting labors for a month and then quickly unassign them so they won't sleep outside all the time, then I can reassign them the next month.
I can see at a glance whether a member of the military has all their needed equipment. If not, I can mouse over them and see what they're missing.
With DFHack's enhanced stocks interface I can sort/search for tunics and filter out owned/dump/forbidden/etc so I can see how many fresh, unclaimed tunics there are and if I need to queue up more of them to be made. Same thing for gloves, socks, trousers, cloaks, hoods, and so on. I have 200 dwarves to clothe and I don't want to massively over-produce clothing. I can also easily go through and mark poor-quality armor for melting. The animal stocks aren't normally sortable. I have many, many animals. It is nice to be able to hit search and type in 'badg' and see a list of just the trained badgers I have so I can see how many there are total without having to count them. Also sorting animals by currently pastured or currently caged is very helpful.
When a dwarf leaves a half-eaten meal in the dining hall and it starts to rot I can use 'cleanowned' to get rid of it. Otherwise it is quite difficult to make the dwarves dispose of it. It is also very nice to have the 'deathcause' hack. I had an engraver found dead in the middle of the fort. No idea what happened to him. Highlighted him in the missing/dead unit list and used 'deathcause' and it turned out he died of old age. Whew, no reason to panic.
Dwarf was in a fey mood for a long time and they want gems. We have gems. We have loads of gems. Used 'showmood' it says they want uncut gems. Oh, now I get it. I guess I was overzealous with my jewelers. So I sent to miners out to go dig up some fresh gems.
When building a long paved road I had to scroll through pages of materials to find shale blocks every single time I laid a new section. When building walls and floors, if I just used shale blocks to make a wall and then lay down another section, DFHack puts shale blocks at the top of the list. Very helpful when I've been building a structure that has used over two thousand shale blocks.
Now for years I've played vanilla Dwarf Fortress. I would assign jobs to migrants as they came in, but if I needed to do any major reassignments it would take a while, or I would just assign random dwarves to the tasks and say "they'll train up the skill eventually." To keep things manageable I'd stick to fifty dwarves. With the additional tools it becomes possible to efficiently manage 200 dwarves in a sane amount of time.