How come you're moving to Ottawa before moving to CA? I don't envy you having to move twice in a short time. The neighborhood my house is in isn't as great as I thought it was at first, but strong aversion to moving is keeping me here for now.
To echo what others said and what you seem to have concluded yourself, as long as you try to get a realistic sense of what you can and can't do, interval training isn't going to be any more likely to hurt you than the long runs you've been doing. I think my foot problems have been partly due to overuse from not being able to do anything other than run when I broke my wrist last summer, and partly due to mechanical issues (I'm rather pigeon-toed and otherwise have oddly-shaped, if well-conditioned, lower legs, and I should have gotten orthotics and coaching on my running form a long time ago rather than just the last few months). But other than being a little sore when I've done too much, I can't say I've ever gotten an injury that was caused by a workout involving sprints, hills, fast tempo runs, etc.
Thanks! It's pretty far - it's over a 3hour plain ride if that helps at all. I am taking my cat with me too which just makes it more stressful (for both of us!).