Welcome to the Port Forum and you've joined for the best if reasons. I was hooked on port in pretty much the same way as you - I was given a case of port for my 21st birthday by my grandparents and still have a couple of bottles left 20 years later. Actually, I was given 13 bottles and the extra bottle was opened by the family on my 21st birthday and shared between us at dinner that night. That's when I first learned what mature port could offer compared to other drinks.
The good news is that the quality of the 2009 vintage looks to be excellent. There will almost certainly be some producers who have the quality and the volume to make a declaration and those who don't will bottle single quinta wines. You will have lots of choice and everything will be available in 6 bottle cases. As to the question of what to buy - perhaps I can wait until we know who offers which wines and what the styles of those wines will be. The vast majority of what is offered will be capable of lasting 25-30 years or more whether it is single quinta wine or full blended wine.
There are a small number of quintas who sell direct (Oscar Quevedo, for example) or you can buy through an established wine merchant. The advantage of a wine merchant is that most will then store your wine for you until you need it at a cost of about £5-10 per year. In that way, you don't have to worry about the storage conditions in your home and whether your cellar / under stairs cupboard / kitchen cabinet is too warm for long term maturation of a case of port.
Buying en-primeur guarantees the provenance of the wine. You know that it was bought and has been stored in perfect conditions. En primeur offers for the 2009 ports will be seen about this time next year. However, port auction prices currently seem to dip below en primeur prices about 5-10 years after their initial offer. This may not continue, but you might like to consider hedging your bets by buying 6 bottles en primeur and looking for opportunistic chances to buy another 6 (or 7) 5-10 years later. This is generally the approach that I take - buy some bottles now and more bottles later.
But most of all, if you are close to London then please consider inviting yourself along to one of our offlines in Covent Garden. When we post details in the "Organising Tastings and Get-Togethers" section, these are open invitations to anyone who wants to join us. As a guide, you would be expected to pay about £35-40 for your meal (or turn up after the meal and then just pay about a £10 share of the corkage fee) and bring a bottle of port with you. If you don't have a bottle of port that fits the theme, just let us know and someone will help out. You really would be very welcome and would have an opportunity to try a range of different ports of different ages. And bring along your friends as well!