Installing
1) Remove the tape from the back of the element
2) carefully press and hold the pins to the top 2 pins
3) Lay the element down and make sure the tape is secure
4) close the back
Charging
The pad only has 1 element, more expensive ones have 2 elements making it less necessary to line it up. However the pad it comes with works just fine, you have to located the phone up a bit on the pad and the blue light will start to flash indicating it is charging
Seems a bit fat after the insert, is that normal?
Yes. You can mitigate this a bit by removing part of the sticker on the element in the phone. The sticker on the side facing the back can be removed CAREFULLY and then put the back on and it will be a bit slimmer.
There is no element available that will work perfectly with the original back, there will be even with one of the stickers removed a slight bulge.
The "Official" Wireless back is much thicker than the original one.
So if you buy that one, the back will be even thicker. I use the kit you have with a case without any issues.
How fast does it charge?
Slower, much slower than using the AC adapter and cable that came with the phone. That is because wireless charging is not as efficient as a direct wire method. It does charge well enough for me as I tend to use it to keep the phone charged rather than trying to charge the phone from near empty to full quickly. If you need to charge full quickly, use the wired charger.