Yeah I think you definitely want the wide angle lens, especially for the front. I have one with the rev B lens.
Lens extension would allow you to mount the lens separately to the camera - for example sticking the camera to something (like the back of the rear view mirror), then mounting the lens on the windscreen - less clutter and a more stealthy installation. I didn't bother and just have mine on a suction mount behind the rear view mirror so it doesn't obscure my view.
I didn't bother with a super capacitor - not sure why it would be needed as it has an internal battery.
Edit: ah - it replaces the battery!
Not sure what the hardwire kit is - it doesn't seem to say but I suspect it's something like what I have done.
I installed mine into my Octavia with a 3m USB cable, piggyback fuse and 12V -> 5V USB adaptor (see
here). I also ran a USB extension cable from the other output to the cubby hole under the stereo for charging my phone. The fuse I piggybacked was the rear wiper as it comes on with the ignition and I have the camera setup to start recording when it gets power and stop when it's switched off.
Bought mine from banggood.com by the way - currently £50 on there (or £46 if you want to wait for it to come from China).