Recruiting and casting separate actors for each part is time-consuming, especially because most actors cannot product quality lines with the equipment or talents they have. This limits your potential actors to a small pool of busy semipros. Usually it is wise to go to semipro VA communities and hunt for work-for-free talent there.
Each actor will need to be supplied with their lines, a contextual script, and pronunciation guides, as well as background on their character and the setting.
Once parts are cast (months, probably), you have to stay on your actor's cases to get all their lines in. Some will drop out. Others will produce lines of unacceptable quality. Retakes will have to be done, of individual lines or whole parts.
Once lines are actually in your hands, they must all be normalized, cleaned, and post-processed in Audacity, adding radio noise and message beeps as appropriate. They must all be properly named, added into missions, and checked in-game for audible volume.
Like all projects it takes twice as long as expected even when well-planned.
Additionally, you (the project leader) will leave it hanging for weeks or months at a time as you become busy with real life.