30 meters (100 ft) should be fine. The bar setup will be essentially 2 line but here are a couple of options: 1) Pegas kites has the Wing Warp system that can be retro fitted to most kites and allows it to be depowered. You will want to check with Pegas Kitesports to confirm the fit for the Firebee 8.5. 2) Consider the Spider Bar set up. Allows a foil to turn faster when setup on a bar. As always you sacrifice brake control when on a bar but the spider bar will effectively help to turn the kite faster. It's a simple fix and will cost you about $10 CDN.
Visit www.boostkiteboarding.com for a pic of the spider set up and WinnipegKiteboaders, a Yahoo group. There is a good set of pics in the Photo section under Spider bar.
Good Luck