Excellent choice of aeroplane. Good quality kits with no nasty resins, and great 'planes to fly, though my preference is for the sportier models.
I have an RV-4 and am building a -8, so may be able to help a bit.
Engine servicing is as much as your inspector allows and is authorised to sign for. You can do the regular maintenance and sign it off yourself. Changing a pot, or the like will require a signature from an inspector approved for such.
There is an RV-9 being built near me with the Wilksch engine. The idea is appealling, but the reality of putting a new engine design in an aircraft means lots of work and maybe doubling the build time, Putting a Lycoming in is simple and straightforward in comparison. You can get mods like injection, electronic ignition and FADEC approved by a reasonably simple procedure that would be a nightmare for a CofA aeroplane.
PFA charges about £50 for registering the project and about £480 for first permit issue. Permit renewal is £160 plus any inspector's fees. Insurance about £1200-1400 for full, or about £500 for liability only. Fuel, hangarage/parking will vary depending on what/where/how.
A Europa will probably use about 15 l/hr against about 22-25 for an RV-9, but (given the record of Europas), I expect insurance would be less. I quite like Europas, but given the choice, I'd opt for the RV.
Have a fly of both if you can. It'll probably make your mind up for you.
Feel free to PM if I can help any more.