Approx 20-40% are in Full-time melee squads. Embark with 2-4 military dwarves depending on biome. They train fulltime and recruits are brought in based on immigrant skills and/or preferred stats.(Higher end of strength,agi, recovery, and disease resistance.) High recovery AND disease resistance are put into a anti-biological warfare squad for those nasty fb's and as an elite last line of defense. Once 2-6 legendaries are made i set up training squads of 2 legends+2 recruits. Graduates are put into a minimum of 4 6-dwarf squads for foot patrols and general use. Excess are tossed into extra training squads and 10-dwarf reinforcement squads.
All Haulers{NEVER FOOD}, Furnace Ops, processors are put in a metal marksdwarf uniform and typically are stuck with shoddy copper gear early on. Each is given a Hauling or processing job to do while off duty. After spending a season shooting at wildlife/prisoners the squad is set to 5-active and left to train and work until needed. This gives you a massive hail of bolts for those nasty sieges. List of jobs is Wood burner, plant gatherer, miller, Plant Processor, Furnace Op, Bone Carver, Glasworker (Block mass production) After a squad or two graduate to full-time legendary status all rank 14 marksdwarves will be moved to a hammerdwarf squad to round out their training. These work as your shocktroops due to their massive agi and tendency to shatter bones.
All the Artisans, [Forgers, Jewlers, Doctors, Farmers, Masons, Mechanics, Bookie/broker, Carpenter, Etc.] Are put in a high-priority Metal Marksdwarf uniform and temporarily activated so they run around in quality armor and are protected from assassination.
You end up with around 80% active during a siege but if you keep the ammo stores stocked from the tree farm and refuse piles you tear up everything.