I've got the S350D SE LWB, I'm a chauffeur so these things are the car of choice really. Since the day I got it, its been an absolute dream, ive racked up 5,500 miles already and not a single niggle bar one, my rear passenger internal handle seems to have stopped opening the door so I'm going to pop into MB on monday and get them to sort this out for me, ive only just found this out.
Like yourself I pretty much went with all of the options ticked, spending as much time as I do in the car, I want to be as comfortable as my clients in the back. This is my second S Class, I had the previous W212 model (in my profile pic) so I'm quite used to the size, they just completely command the road that no other car (except possibly a Bentley or a Rolls) can even come close to competing with. Some guys who work with me have 7 Series and as nice as they are, the S Class just shines above them.
Im sure you will get used to the size straight away, they just drive themselves, so quiet, so smooth, they really do just glide along perfectly.
The only thing I went for was the Star Guard, with work i like the car to be clean at all times, this just helps give it that extra little sheen. Though to be fair, with how the weather has been these last two weeks, keeping it clean has been a pain in the backside.
I don't have boot mats but i did go for a boot liner, Mercedes don't supply these so it s from a third party company (google will point you in the right direction) Its just a nice rigid pvc liner that lays in the boot and protects the interior, if it gets dirty you just lift it out and give it a wash over then stick it back in.
I did buy myself a small 1TB HD which has all my music loaded on, and is neatly plugged into the car via the USB port in the front centre arm rest-compartment. To be honest other than that you don't need much else as its such a perfect car it pretty much ticks every other box itself.
I bet you can't wait..