Karen, travelling abroad so far has been fairly straight forward, although I've still to do the coming back to the UK part. The DEFRA website provides all the info about the pet passport scheme. Like Sue mentioned after a succesful rabies vaccine you can take them out the country but have to wait 6 month before you can return to the UK; therefore I'd say you probably have to start the process approx 8 month before your planned vacation. To get a passport they must be chipped, have the rabies vaccine, then they are tested to see if the vaccine was succesful, then you can get their passport.
The only glitch I came across, and I believe it was Lyn on here that had the same problem was that my vet insisted that although Brodie had a 3 year vaccine because we were taking him to France he required the vaccine yearly. The vet was incorrect on this. The dog has to be resident in France for 3 consecutive months before it is considered a French resident and has to follow the French regulations. DEFRA has a pet passport helpline that give you advice on the passport and the UK regulations. They will also give you contact numbers for the embassies of other countries if you want to call them for specifics. I called the Belgium and French ones as there was a possibility I'd be traveling through both countries.
I also traveled through the Eurotunnel and would recommend it. We arrived early, got on an earlier train, sat in the car the complete trip, and 30 minutes we were in France. With regards to the ferries we have never used them with Brodie but different operators offer different facilities. Superfast ferries used to run an overnight ferry from Scotland to Belgium. In addition to kennels on a deck, which had 24 hour access, they also had pet cabins which you and your dog shared. Unfortunately for us the crossing has been taken over by Norfolkline and they only offer the kennel option. So it is worthwhile checking what each operator offers. The DEFRA website provides a list of authorised pet crossings along with the operator.
I plan to use our local vet in France to get Brodie treated before returning and I've brought his worming tablets with me. Again the DEFRA web site details what treatments are required and what sections of the passport nead to be marked up and stamped.
We stayed in Folkstone the night before our crossing, the hotel was one that was advertised on the Eurotunnel website as pet friendly. However in France we drove straight to our home so I've no experience of hotels abroad. I've emailed a friend who travelled through France to Spain with two dogs to see if she has any useful info for you. My only input would be it's a lot hotter in France and Spain than the UK so think about air-conditioning in the hotels. The hotel we stayed in at Folkstone was a nice enough large old hotel but we were put in the attic (probably where all dogs are put), it was 30 deg outside; the room was roasting; we couldn't open the window for worry of Brodie jumping out; he panted and paced all night; thus the reason we arrived at the Eurotunnel early - we'd given up trying to get any sleep!
You'd have to think about insurance too if you're current pet insurance doesn't cover them abroad. From the insurances I looked at for Brodie, most didn't cover treatment abroad. With us having a home in France it was something specific I looked for when taking out his insurance.
After having gone through leaving the UK once, other than the glitch with the rabies vaccine confusion, it really is straightforward.
Hope Tilly is well.