I'd like SOME immigrants but don't want the repetitive grind of building hundreds of new bedrooms; that's more like micromanagement hell than fun, imo.
I really enjoyed the slower pace and getting to know fewer dwarves individually; especially the Hunter trying to fell Boars with wooden crossbow bolts 
Yes, it is. There used to be a delay in pop cap taking effect (tied to the yearly diplomat visit), this has been removed. I enjoy 20-30 dwarves most. Just enough to cover all industries with specialists and manageable enough to play really longtime. The default settings lead to 200 dwarves in 3 years and abandoning the embark soon after due to fps loss. Above 30 I start to lose track of my dwarves. When you get kids (and don't prevent that by strict pop cap) you can increase population pretty fast (a few years for births + 12 years to grow up) to 50, 80, 100 and higher from that starting level even with only a few couples. Pop cap itself can be easily changed and adjusted after world generation in a running fortress, if you want to. Pop cap massively changes gameplay (especially with low pop cap, but much higher strict pop cap, i.e. a sizeable fort grown biologically), without the option to substitute all losses with seasonal migrants you end up playing much more careful and with attention to detail. No more carelessly drowning half the fortress every other year or sending them unprepared to greet invaders.