At the moment on my cyclocross bike iam running 10 speed campanolo shifters with 8 speed shimano mechs (it works very well for those that are wondering!). I want to upgrade the rear cassette to 9 speed (its a touring bike as well) but also want a new road crankset.

Question is the new shimano 105 5800 cranks are a good price and just what i want (in compact) but they are 11 speed. Will they work with a 9 speed chain or would i need to get some spacers to move the inner chainring out a little as the 9 speed chain is wider?

They’ll be fine, although why not go SRAM, just to introduce some more complexity to your drivetrain 😉

Then fit one Rotor ring.

haha, that would be great. SRAM, campagnolo and shimano all working in harmony. Definately going to add in a KMC chain for kicks (and because they are the best)