Nike Plus/ EA Sports Active 2/ C25k/ Slendertone

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OK so relatively unfit just starting up -sit behind a desk all day. Started last week with the EA Sports Active 2 3 weeks cardio challenge. I also have Slendertone Arms and Abs - I know this doesn't burn calories in reality - however it has made my core very strong and can see the difference in my arms. They work but only up to a certain point. Looking to start doing C25k in the mornings tracking it with Nike Plus app on iPhone and the NHS C25K podcasts. I'm eating back my exercise calories after reading on here before starting, and working on 40/30/30 split Protein/Fat/Carbs currently.

Do I have to be worried about over training as I'm coming from basically zero fitness? Have noticed the time I'm walking/jogging with the dog increasing every morning anyway before. My thoughts were I could wear the Slendertone Abs belt whilst doing the half hour of C25K 3 times a week, leaving the 4 times a week EA Sports Active 2 - around 20 mins or so daily. If I have 1 rest day and 1 day where I do both of them is this overkill?

Quite enjoying the cardio and want to do as much as possible but in the smartest way possible rather than overdoing it by being too enthusiastic