well it was baking hot every day, except today which was a bit cloudy (13 degrees); shorts and t-shirt did just fine. however, as people are indicating it depends on your abilities to deal with weather. obviously mountain areas are changeable, and generally chilly first thing in the morning and during the night. I tour during the winters a lot (usually heading to where there is snow), so I have decent equipment (ie sleeping bag, tent, etc) which can make a big difference.
I spoke to a local in Beget, and he said it's 'once again' unseasonably warm, and they've had very little snow this winter. it seems they are going through the reverse of the Scottish Highlands weather change (which oddly, he knew about).
in answer to your original question, I think yes shorts and shirt are going to be fine for cycling (wearing the paclite if it's chilly). if there is some late snow, then you're probably going to head a different direction anyway. I'm assuming you won't ride into a snow storm with shorts and a t-shirt
There's a well stocked bike shop at Ripoll near the train station, if you feel the need to get more clothing. The road from Castellfollit de la Roca (via Oix) to Camprodon was fantastic, but very up and down. Camprodon is nice (the crepe place in the middle of town is very good), the campsite 2 km's south looked ok but the campsite 2 km north looked awful. Beget was an interesting little place too, it has a hostal. Campsites were around €14/night.
if you wanted to skip the urban sprawl of barcelona, then the train is a quick and cheap option. barcelona to figueres was €10, and ripoll to barcelona was €7. I imagine getting to the outskirts (Granollers) would be a few euro. you can just walk on the Renfe trains with the bike (they are much wider trains than in the UK).
have a good trip...
cheers
