"Do you need Cofa or will a N-reg Experimental do the job? If I recall correct, the Pitts runs under N-experimental and need permits every 3-6 month to stay in the EU? "
Pitts aircraft come in both factory built CofA and permit. I recommended a factory machine similar to the one used by Northampton school of flying. The Cap is in use at aeroclubs all over France but is probably more of an intermediate trainer than a novice mount. The Decathlon is not a very good lead in to Aerobatics or "vintage" TW in my opinion. I would recommend avoiding the TW requirement and going for the Robin as the low cost proven solution.
Rod1