Jan,
It's up to you on when you subscribe. I wouldn't recommend installing JFBConnect the day you launch as there are a lot of options for configuration and it can take some time to setup. However, it can definitely be added to a site as one of the last features.
As for discounts on one year, we don't have a 1-year plan. However, we do provide a 25% off discount on renewals if your subscription is still active. So, before your subscription expires, you'll be able to resubscribe again for another 6 months at $45.
There are also discounts on our 'Social Bundle', which is JFBConnect and JLinked, for LinkedIn, combined.
I hope that helps answer your questions, but if you have others, just let me know.
Thanks,
Alex