I've always wanted to attend an away game at Catalan and the timing seems right for next year, 12th July.
I've stayed in Lloret a few times and seen other fans there for their away game and I believe that many Wire fans use Lloret as a base and catch a coach to and from the game.
I would probably go to one of the resorts along the coast, Lloret, Calella, Tossa del Mar for example staying midweek to midweek, either side of the 12th July, and I see that coaches are available from multiple resorts.
Do many Wire fans get picked up at places other than Lloret? I don't particularly want to stay in Calella for example if I would be the only one waiting for a coach.
Any other advice would be welcome.

You pretty much answered your own question. Lots do the Lloret thing, the Rhyl of Spain or it felt that way the last time I was there. A lot do stay in Perpignan some decent bars and restaurants and no traveling to do because you already there. End of day it depends how long you going for and do you want a bit of beach holiday.

If you stay in Perpignan, as we always do, you can also use your match day ticket to use the public transport too and from the game for free

I've stayed in the Lloret area many times, normally choosing the Fenals beach area as it's a lot quieter, cleaner and nicer than Lloret itself. In fact the only nagging doubt I have about staying there in July is that it's likely to be mad busy and kids everywhere.
Staying in Perpignan is something I hadn't thought of. Is there much to see and do there on the non match days? I believe there is a beach resort not too far away. Would a week be too long?

A week in Perpignan would be too long for me personally. It’s a nice place not a typical holiday destination but ok for match weekends. I’d be tempted to go to Barcelona if going for a week you can get a train from there.

Canet is the nearest beach, 45minutes taxi 1 hour 15 bus, beautiful beaches, also if you have time jump on a train from Perpignan to a fishing port called Coulier, I think that’s what it’s called, stunning place