To answer some of your questions from my own perspective:
Where did you book it?
My first Euro trip I booked with Track Sense. Their not the cheapest company out there, but it was a great crowd and well run event and continued to use them for a good 4 years after my first trip. Focused Events have a lease at the Almeria circuit in Spain, and also run other Euros, and are better on price. Experience can vary with them as does the crowd who go, but I've used them a few times with very few issues.
What was included (bike transportation - how convenient is it?) Can you get it from London?
Bike, spares and kit transportation is all included in the price. Drop off locations vary, for Track Sense the main depot is in Sandy, Bedfordshire, and Focused is in Pullborough, so a couple of hours from London, no issues.
Did you book flights separately?
The packages usually include bike/kit transportation, the track day itself, shared accomodation (2 people to a room, you can hire the room for yourself at extra cost) with breakfast included. The rest is all down to you, so flights, lunch/dinner, petrol, insurance for the track etc.
Check the websites of the respective companies.
Dos and Don'ts
Do have fun.
If you can afford tuition, it's worth it.
Don't take it too seriously.
Take spare tyres and the usual bike spares in case you have an off and need to get back on track. although spares are sometimes available depending on the circuit you're at and the support.
Enjoy the overall experience.
Very subjective, but in my opinion, depends on your level of track riding experience, who you're going with and if you're going for some fun or to get better and improve your track riding. I've loved every trip I made out there over the past few years, but haven't been in just over a year and do miss it. Try it once, it's definetly better value than UK days with all the heroes and unpredictable weather. If you don't like it, you don't have to go again.