Hi Patrick,
Firstly, the 512G is a good dash cam - I have one myself so can vouch for it.
Don't worry too much about the parking mode - the camera isn't designed to be on all the time as it would drain your battery. The 512G has a built in rechargeable battery and a motion detector so if there is movement around the car it should detect it and run on the internal battery.
They're quite easy to install yourself using the fusebox. You just need to find a fuse that comes on and off with the ignition and preferably is not for a very important function. Halfords use these fitting kits:
http://www.halfords.com/technology/dash-cams/dash-cams/nextbase-incarcam-hardwire-kit
You could do that yourself - it just plugs into the fuse box once you have located a fuse to use and you can earth it to a bolt etc. Hardest bit is running the wires behind the trim in more modern cars but it shouldn't be too hard.
Hope that helps