Depends a lot on the fleet. TDY long call reserve and how far you have to go. 737 is very dynamic. 777 not so much and more predictable.
I can sit long call in SFO for ORD. Short call, time to go out. Book the flights, call and get them authorized. Easy to do. Set up transportation with crew accommodation, and sit short call in your company paid hotel.
Book the flight as soon as you know your going. Getting a seat assigned is a bit more of a problem the closer to departure you get.
How many days off? Again much depends on the fleet. I would say you would probably work more on the narrow body, less on wide body.