Is it possible to just use one bar for both the 9m and 16m waroos, and if so which would you reccomend the 45cm or 55cm bar?

The 16m Waroo isn't out yet, so I can't say for sure. I would think that you could use either bar with either kite. If you only want one bar, go with the 55cm so the 16m turns faster. I'm sure that size will still work fine on the 9m. We have been flying the 9m's with our own bars(Slingshot, RRD, etc..) all sizes, and it works great.