Been there, done that. Mine's a D8, though there's not much difference in terms of the seats really.
I can't be sure on your first question, do you mean the bench isn't split, or the backs?
As for the electrics, it's all a bit of a faff. The first thing to do is get a 12V feed from somewhere. I took mine from the engine bay fuse box, since it's meant to be a good 30-35A max current. I pulled my cable through the grommet in the passenger footwell, it's the blue cable in this picture:
I took a ground cable from the earthing point underneath the stereo.
I then built a splitter with inline blade fuses and attached that to the end of the blue cable:
The passenger seat won't be a problem, you just need to supply 12V and ground from one of the splitter outputs. If you're lucky the wiring will be in place, I'm not sure on the plug colour since I believe it's different on the D9. Mine had this bunch of cables, including 12V/ground (unused on the cloth seats) and the airbag pretensioner (orange plug):
As for the driver's seat, the memory system will not work without the electric mirrors being installed as well. That is known to be a horribly tricky thing to do, since you've got to try and get 10-12 wires through each of the front door concertinas.
A far easier solution is to do away with the seat ECU, and splice the loom such that the switches are wired directly onto the motors (bypassing the ECU). I had a pin map somewhere but it was wrong - I highly recommend using a set of terminal blocks and some trial and error!
You also have to solder two additional ground lines to the switch panel, these are the two thick red (sorry, only colour I had) cables here:
A fairly big job, especially if (like me) I didn't really know what I was doing. But it's been really worth it, have done 20k in the car with the new seats in and they're so much nicer than the cloth. I've also wired up the heated seats which are wonderful in the winter!
