Maybe a mistake everyone has to make for themselves (you probably won't believe anyone who tells you), but don't go nuts buying a bunch of gear too quickly.
Try (rent, borrow, convince shops to lend) various BCD's -preferably very different styles - and see which one you like most.
In jacket style BCD's there's lots of different features, styles, sizes, etc available and then there's the BP/W style which is totally customisable to suit all types of diving.
Horses for courses so try as many as you can - if you don't find which features you do like you might at least find out what you don't like.
