You pretty much always have to sail up wind when you are in the lee of Grenada (no mater the time of year I think) as the winds whips around the top of the island. But don't imagine you will spend much time sailing up the cost of Grenada and want to spend more time on Cariacou and in the Grenadines. I have only made it as far as TBC but with 11 days and a one way trip you should have lots of options and can make your way leisurely north. The passage from George Town to Carriacou can be rough but after that you can sail in the lee of most islands - a stop at la ronde island is a nice break. Mystique may be a headache to get too and the passage to Bequia and then to St Vincent may not be fun either.
you will be fine and sounds like a great trip.
.. sigh I miss sailing! I miss talking about sailing!