I fitted my Nextbase Duo myself in both my cars ( I bought a second GPS mount and hard wired into a permanent live I found up above the interior light ) simple . The camera does not drain the battery when parked ; I have left the car over a week without difficulty .
I would venture the OP almost certainly will have issues with an E63S on the power situation!
Modern Mercs are right on the edge and any small current drain upsets them.
I didn't wire mine into permanent live as my car lives at work or in a garage - I'm willing to take the risk on the small number of times it is not in either location.
However, if I was you OP I would consider the additional battery pack or keep the car on a trickle when not using - or don't wire into permanent if you don't need it whilst parks.
I fitted BV 650s into a Nissan Juke and Seat Altea and it was very easy if you are the DIY type.
I got mine done when I had audio upgraded as trim was going to be off anyway but I never had to remove anything to do the install in the above cars.