To answer your questions Ron:
1) We learnt about the weight check as part of the standard PADI OW course, but in the first few dives when I sank doing it we just continued the dives over-weighted and I did all the skills just fine within 3 CW dives. It was only the last dive that I did on Wednesday evening that I decided, following advice from this thread, to do the weight check properly and this helped my control underwater more than I though it would.
2) I understand everything in the OW manual about tanks etc, but didn't really know what I was using. I do now though, in as much as it's a 12 litre steel cylinder.
3) BCD Sizing. My only criticism of what's been an excellent dive school/shop is they seem totally mixed up with their sizing. When I signed up for the course I had to fill in a card with my height, waist, hips and chest size (I'm a fairly normal 5'10", 30" waist and 36" chest). However, when I turned up for the course on day one they took one look at me and passed me a large wetsuit and a medium BCD. I absolutely froze in the large wetsuit, and was shaking quite a lot even before we went underwater for the first time! They didn't have any wetsuits for hire smaller than large, so I had to buy one. Again, when buying one, almost all their suits were medium or above, but thankfully they did have one small one on the shelf which fitted me well. The oversized BCD I never really questioned as I'm a novice and didn't really appreciate how important the fit was; I didn't complain and just thought a bit loose was ok. However, this thread got me looking at BCDs online and I discovered that the Medium size one I'd been using was intended for someone of about a 38-40" chest. Changing to a Small size made a surprisingly big difference and did wonders to how relaxed I was underwater. Again, a learning process for me - I am a complete novice at all of this. The final thing to mention about the sizing was a drysuit orientation dive that I did in the pool, where I was in a drysuit so big (XL I think?!!!) that I sank in it without a BCD on, which was a very un-nerving experience. That was the 7th suit I'd tried on - all the others were so big I could get my hand and occasionally my whole arm down the neck! Wearing the huge drysuit was such a horrible experience that I cancelled my UK OW and decided on a Referral instead on my forthcoming holiday.
To be honest though, these are minor gripes. The instructor I had was absolutely brilliant, as were the divemasters. Also, the members of the club are all friendly and welcoming. The swimming pool was brilliant, and quite deep too which was great for learning. I got 100% in all the tests and final exam, passed all my skills easily on the first attempt, and have spent two dives practising those skills again, so the whole learning experience has been very positive indeed. In retrospect, the sizing and weighting has been the only bad thing really; I'd have been fine if I was 6 foot tall and 14 stone, which given their kit supply I presume most of their clients are.
Now I'm in the correct size of wetsuit and BCD with the correct amount of weight on me I'm very happy. I still can't stay upright, but I'm sure with some more practise and my own equipment that will come with time.
That seems like a silly move, but maybe most LDS don't have an adequate supply of BC's of various sizes? Seems like the students would notice, but maybe they are overwhelmed? Well the fun really starts when you get in Open Water! 
