1. If I do build an RV-9 could I fly airways (if suitably equiped)???
You are restricted to daytime VFR only.
2. Could I take it outside UK??
The permit will say you need permission of the state you are visiting. In practice a standard agreement exists to let you just fly, the exceptions being the Channel islands, Belgium and Spain, all of which will let you in but you have to write in advance.
Rod1