Sorry, it's probably not what you want to here but I agree with other people here saying to postpone for all the same reasons.
If you haven't got the aircraft confirmed yet you must check that the school/club will let you rent without knowing a thing about how you fly. Most will require a club checkout.
You should do some more research and questioning on the UK and European rules and regs. For example, knowing about the schengen area and what it means for your flight. Specifically for your first landing in the EU outside of the UK.
I personally wouldn't be TOO fussed about the differences between pipers and cessnas etc. These are light aircraft and require a knowledge and appreciation that they will andle differently and have their own quirks, but I would say (assuming the rental place lets you rent without a checkout) doing 3-5 circuits on your own would probably be enough (along with a decent studying of the POH beforehand - I believe in knowing as much about the systems before flying a new type as possible as it puts you some steps ahead if anything unusual should happen).
Here's one where people might disagree with me. I think doing the flight without a GPS is masochistic. It can be done of course - but you will save yourself a lot of time and bother, and again put yourself ahead of the game by using one.