It all depends on your flying. If you fly IFR, no surprises will be met. If you file VFR, plan to avoid Barcelona and Tarragona by all means and wider than you would usually do it. There are VFR-corridors around Barcelone, but basically they will try to put you on 1000 ft AGL and follow the VFR-corridor 20-40 miles outbound of Barcelone. I usually fly over the sea in order to avoid Barcelone.
Actually, if you wanted to file VFR, you will need the charts to avoid certain airspaces.
For a fuel stop, France is definitely cheaper and more suitable than any airfield in Spain. Get information on the opening hours and fuel availability before chosing your airfield. In France, very often you need a fuel-card and on Sundays some airports might be closed.
My favourite fuel stop is LFMZ, Lezignan Corbieres. No traffic, only one friendly controller and very fast service. If you file it only as a technical stop, you will be able to continue on your flightplan.
French controllers are easy to deal with and if you just tell them you fly on the coastline, eventually before crossing the border, Toulouse will hand you over to Girona. Max VFR-altitude in Spain is 10000 ft.
If you fly VFR, try to overfly the Pyrenees at the coast, where they are still shallow. The tend to have some nasty weather, CBs and turbulence further up North, even if 30 miles before and after the weather is absolutely fine.
When overflying the Med, make sure you have studied your charts as you will be vectored to waypoints by Palma approach and then to Son Bonet. LESB is a GA-friendly airport, you will need a safety vest and you will be checked by a friendly policeman if it is your first landing. Have your documention and passport ready.