Rest days are really important and aren't counted at the 30 days. How many rest days you take is up to the individual but most trainers (including Jillian) would recommend 1-2 a week. So perhaps extending it to a 6 week challenge would be a good idea??

I plan on taking one enforced rest dy a week, and then if anything comes up, if I'm too sore or if I just can't do it I have a spare.

I think extending it would be a good idea to allow for one or two rest days a week

Sounds good!