CFB Gagetown is a magical place. If you have or can bring a vehicle, do so. You're about 20 minutes from Fredericton which is not too bad for a New Brunswick city. Oromocto, on the other hand, is dull as dish water. There is not much to do there, mostly a bedroom community.
As for gear for the field, be sure to bring warm stuff. I remember being on my FOO course in 1992 and freezing at night in Hersey impact area in the middle of July. Bring your combat gloves (don't assume you won't need them) and I always brought my wooley pooly sweater (or something of the like) since it would keep me warm on cool damp summer nights.
A bug bar and a lot of bug juice is essential because the mosquito factory in the training area will eat you alive. I don't know much about M-5 or M minus five, as we used to call it after it first opened. I stood duty there a few times but I lived in the Sgts shacks, so I couldn't tell you much more. It does look like a prison. Good luck.
PJ D-Dog