This is really helpful, thanks. I just spent lots of time googling and reading based on the pointers you all gave me. Wonderful.

I think for now it sounds like I should keep doing short courses most days, and throw in the odd longer course. If I do courses with hills, it's not full-on interval training, but should have some of the same effect.

I'll look at the more serious training once my basic conditioning is further along. I think that getting too serious about structured workouts too early risks taking the fun out of it.

Do any of you use Trainer Road?