Nine needles will be sufficient for most jobs but if you have the extra money 15 is better. The number of colors per design will depending somewhat on the type of work you do. We produce mostly business logos which generally have 1-3 colors per design with an occasional extra needle used for 60 wt thread with a 65/9 needle. You'll probably want to keep white and black cones on the rack and possibly red or other colors. Having extra needles is nice when you're having problems with a needle. It also helps to prep thread for the next job while running a job.