I would do it in the Spring. I ordered a few figs from Paradisenursery.com. The first fig I ordered was a Petite Negronne, which is the only true dwarf fig. Now I have two Celestes. I believe that a Celeste is a little more hardy if you want to leave it outside during the winter. Also, it seems easy enough to prune it back every year or two, to keep it small.

By the way, is your garden facing the south? That would help, because a south facing wall will absorb a lot of heat and increase the chance of survival. My outdoor fig is not near a wall, but wrapping in burlap worked last winter.

I also grow Petite Negronne. Nice, small, even had a few figs. I have bought it from Wayside Gardens. Very good nursery with great plants (a little bit expensive, but sign to their website and you will constantly have promotion emails with really good prices).