(note I did the full, which is in October, but I think my answers still apply):

I would recommend staying in Calella for maybe Friday - Monday for convenience. Yes the logistics are easier for a half, and it looks like the half runs inland, instead of following the waterline like the full. But you're talking an early drive in, and there are basically two ways: the toll freeway or follow the coast, which is a bit slow due to all the roundabouts.

Not really unless you want a lot of time to sit on the beach. A couple days are good. Keep in mind for the races, 70.3 in May and full in October, they are off the peak vacation season so it is very very quiet in Calella.

I haven't ridden it but the course for the half goes inland so you should expect a fair amount of hill climbing. Downhill finish though.

They seemed pretty similar to me although Barcelona, being a major city, has a wider variety of options - either more or less expensive.

Depending how long you're staying - think about getting a self storage unit for the bike after the race. I used City Self Storage and they were easy to deal with. It's easier if you speak some Spanish but not required. I can't remember, check a map, but I think you want their location near Hospitalet if you want the bike kept near the airport.

That's about it off the top of my head.

Thanks a lot Spudone. This is really useful information and much appreciated.

Spudone pretty much covered it all, I did the Half this year, I suggest staying in Calella for a few days over the race Weekend, it is nice enough for a couple of days and saves an early commute on race day.

There are plenty of hotels on the front and lots of reasonably priced restaurants.

The course is straight forward, three climbs, steady and not too dramatic, one technical 5km on one of the decents that you need a little caution on, suggest driving the course as always, the run and swim are flat though.

You can then enjoy Barcelona.