Another option for diving a wreck (as well as seeing barracuda etc) is to dive out of Palamos which is a little closer to Barcelona than L'Estartit. The wreck "Boreas" is a 5 minute boat trip from the Palamos harbour and is in about 30-35 metres of water. You could do your Deep specialty with a shop there. For barracuda and other big fish I can never go past "Canons de Tamariu" which is a little further out of the harbour but an absolutely spectacular dive.
I have dived out of Palamos through both H20 Diving (
H2O Diving Center - Palamos) and Palamos Dive Centre (
Palams Dive Center. Centro de submarinismo en Palams, Girona (Spain)). Personally I like the boat that Palamos Dive Centre use better (it is faster and more comfortable in my opinion) but I'm not sure if they speak English. I know that the Dive Centre Manager for H20 Diving speaks english as he is an ex-work mate of mine and a great guy. He also captains the boat from time to time. That said, I'm not sure about the DMs. Both centres have loads of younger people diving with them. I can't remember if they have nitrox at either shop.
I don't think you can go wrong with either centre.
In L'Estartit, I have dived mostly with La Sirena (
Diving Center| Medas Islands| l' Estartit| Catalonia| Spain) and Aquatica (
AQUÀTICA. Submarinisme. Submarinismo. Buceo. Plongée. Diving. Tauchen. Duiken.). La Sirena takes out A LOT of divers on each boat. I'm guessing they have room for 20 + divers for each trip out. Aquatica on the other hand has smaller groups. I can highly recommend Aquatica and their DMs and Captains. They all speak english as far as I'm aware and are a great bunch of people. All the shops in L'Estartit use the same communal compressors for air and they all have nitrox.
La cova de la vaca and the 2 dofi sites are the "cave" sites (they are really tunnels that pass from one side of the island to the other) in the Medas. The boats and centres have a monthly (I believe) schedule so that there is always only one boat at each site. So depending on the days that you are in L'Estartit, you have to pick the right boat to be ensured that you go to the dive site that you want. You can ask at the dive centre who is scheduled for which site on which day at what hour...
In terms of wetsuit, I'd agree with WoodyLompoc, a hood is going to be necessary unless you don't feel the cold. I use a drysuit until June (I feel the cold) and then a 7mm semi-dry until November when it is time to switch back to the drysuit (I'm a real baby when it comes to cold!).
Enjoy your trip and let us know if there is any more information that you need!