I don't understand why you couldn't have the OE pads without leather if you so chose. BMW call it imitation leather, not vinyl, in the realoem link. We had heated seats on several BMW vehicles without having leather.

Can't help with the installer, maybe an SFB area resident can help.

Yes, you can wire the aftermarket pads to the OE switches. Or install aftermarket switches. Aftermarket switches re likely cheaper, but they look aftermarket. Your call.

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2007 X3 3.0si, 6 MT, Premium, White

Retired:
2008 535i, 6 MT, M Sport, Premium, Space Grey
2003 X5 3.0 Steptronic, Premium, Titanium Silver
2002 325xi 5 MT, Steel Grey
2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue