@OP: alright, that really sounds like quite a lot
no reason for special walking then. if you want to start doing more cardio, that's still highly recommended because of its myriad of benefits. but it doesn't seem "mandatory".
@phone as a tracker: as i said, it depends if you have a a specialised "motion sensor" in your phone or not. if you have, then battery impact of using your phone as a tracker will be minimal (because the sensor is super low energy and running 24/7 anyway). if you don't, then the impact is large (because your main cpu has to stay awake to do part of the tracking).
@withings: yeah, i like the look as well. i thought it was more expensive than it is. still feel like it's very overpriced based on its capabilities, but yeah, the price difference is a lot lower than i originally thought.
@step tracking in general: if OP is already moving around quite a lot anyway, i don't see much benefit of buying something to track his steps. the upside of OP doing 50% more walking will be very low, compared to alternative uses of his time (strength training, yoga, flexibility, swimming, biking or whatsoever). at least that's my guess.