During the Summer of 2004, my wife and I decided on the same trip however she didn't fancy the long ride down through France. As we live in Kent, it seemed logically to use the Dover-Calais ferry crossing. We got around that by booking her a cheap EasyJet flight to Barcelona, and I took a couple of days to get down there. The first night, after staying on the minor roads which are naturally slower than the autoroutes but far more enjoyable, I stopped at Saumur in the Loire Valley. Just stopped at the first pension (small hotel) and booked a room. Next day I rode down to Flourence near Toulouse and stayed at the holiday home of a neighbour. The next day it was a quick ride down to Perpignan and the autoroute into Barcelona. The city was frightenly hot and very confusing so I eventually gave up, stopped and went into a shop to ask for directions. By chance I was 1/4 mile from the main square in the city. In the square was a Tourist Information Office and the staff found a budget hotel for me a few hundred yards away. Booked in, locked the bike up outside, got a bus to the airport about 10 miles west of the city, and met my wife with minutes to spare.
After a couple of days in the city - yes, it is a fascinating place, we rode up to Manresa, do see the monestery at Monserrat on the way, and up the Pyrenees to Andorra. Andorra was a nightmare and a constant traffic jam with one road in and one out. Because of smuggling - white goods are cheaper - every car seemed to get stopped and checked. First night stop at Sort. Next day up to various cols reaching the stunning Col du Tourmalet (2114m) and often one of the stages of the Tour de France. Stayed the night at a B&B at Argeles-Gazost.
Next day rode to Lourdes and took the A64 autoroute west to Biarritz and the north Spanish coast. We passed San Sebastian and stopped at a very strange hotel on the village of Ondarroa, a bit like a white-washed army barracks with almost no staff and on the cliffs overlooking the sea. It was far to hot to comfortably tour so we stayed there for a couple of chill-out days before riding into the inferno of Bilbao to catch the return ferry home to Portsmouth.
What to take? All the stuff you might take on a UK holiday, passport, E111, bike docs, mobile phone.
Advice? Don't go in July/August. It's far too hot to enjoy yourselves. This was impressed on us a few weeks ago with our trip to the Ardeche. If struggling to stay cool and looking out for melting tar on the roads is your thing then so be it, but we shall be giving hot countries a miss at this time of the year. We peaked htis year at 37C (99F) on the autoroute between the Ardeche and Paris, and that was at 4 in the afternoon!