Lordy I think that motor would be an older model because Yamaha do not sell 2 strokes anymore in the UK. But it does say new with 2 years warranty. So I guess it's just one they have had in stock for while.
Anyway... Whichever set up you go for, I hope you get as much enjoyment from your SIB as I have. I've been boating on and off for over 30 years, but I've had some of the best times with the SIB.
If you're new to boating, do take it easy until you gain a bit of experience! You may want to learn a little seamanship... I would recommend an RYA powerboat course, but the following are also good:
(aimed at yachtsmen but really useful)
(see the 'sea safety' section)
(quirky interface but interesting)
Or a good book is http://www.rya.org.uk/Shop/Cultures/en-GB/g13.htm