Nathalie, I've just looked back to your original post. If you've got a 10k PB of 48 something, and regularly do around 50 min or less, then as long as you've done the extra mileage, and built up gradually with no probems, then I'd say 1:50 is a reasonable target - maybe even 1:45 if everything goes perfectly
A couple of provisos: everyone is different, so you may me more suited to shorter distances, or you may be perfectly suited to half-marathon and beyond - after 18th Jan, you'll have a better idea. From what I remember about the course, it's not easy to run steady pace all the way round, but be careful about setting off too fast - the last mile gives you every opportunity to make up any lost time.
As it's your first half, it's going to be a PB, no matter what time you do, so don't get too hung up about the time - better to do 1:55 comfortably, than struggle for a faster time, and possibly be disappointed over a few seconds.
So, in answer to your question - no it's not crazy. Good luck, but enjoy
!