I trust the dwarves to do the jobs I tell them to do. When I first started, I couldn't handle more than 7 dwarves because I was always checking to make sure that I had 5 more tasks for them to do when that one was over. If I had to go somewhere else in the fort to watch an other dwarf, I'd pause. I'd pause pretty much whenever I or the game did something. It was... really slow.
My current fort is somewhere between 60 or 70. I still don't leave my game running, but I no longer have to micromanage every dwarf. Mostly I do meta-control now, I have a corp of 20-30 or so haulers who do nothing but haul and smelt the orc and goblin armor, smelt the natural ore of this place (literally swimming in sphalerite, malachite, magnetite, and platinum; the richest site I've ever seen short of addy), butcher, tan, process plants, and do pretty much any other task that has no skill modifiers. Meanwhile, my 15-20 core dwarves do important tasks like forging furniture, weapons, and armor, making ammo and totems from orc bones, mining out sphalerite and rooms for the nobles, practicing engraving, putting cloth designs in everything in my fort, farming, cooking, brewing, etc. The only time I need to micromanage is when a crisis hits, like running low on food. Combined with my army of 30 soldiers, there's a lot going on that I really don't worry about any more. It's a lot of fun actually.