In the beginning of my forts, I limit my pop cap to 30. Anymore than that while I'm setting up is too much to micromanage, though I do allow births after that number by setting the strict pop cap to the 250. These first 30 dwarves are treated like kings. I never use furniture that is less than exceptional. The crap gets sold to the caravans while the good stuff is set up in rooms. This starting force basically become my noble class later on down the line. Once I'm set up and confident I can handle more dwarves, I open the flood gates, so to speak.
Useless dwarves usually get thrown into my Hauler/Engraver squad. Dwarves with good physical stats that can handle stress, get thrown into my military. There are some professions I never use, but most others get at least 1-2 dwarves assigned to them. If its something I only use sparingly, they're also co-assigned to the hauler/engraver squad. I find just dabbling in almost everything gives the fortress a nice busy feeling even when I have 50+ dwarves idle. I know some people hate idlers, but I find if I want something done RIGHT NOW, idlers are a godsend straight from Armok.
Of course, this kind of activity used to overwhelm me. I got sucked into the mentailty that idlers = bad when I first started a few years ago. Every time I mentioned having idle dwarves someone would inevitably come along to tell me I wasn't managing the fortress right. So I played with ONLY 30 dwarves tops for a long while. I'm much more knowledgeable and secure in how I run my forts now, though. Don't feel like you have to have a certain number of dwarves or do things a certain way just because the mojarity do. Once I started playing MY way, I had scads more fun. Repelling the old goblin sieges with only 5-6 military dwarves was something, let me tell you! XD