Hi,
It's not a difficult task at all really, especially if you have some experience using Hog Rings and upholstery, and you could farm that portion out to an Upholstery Shop for minimum cost.
But, adding the Porsche system is not the way to go at all.
I am planning to do this if I keep my car and have already sourced the Heaters -
www.heaterseats.com and adding in the Porsche OEM Switches instead of those with the kit - PN# 996.613.152.00 (01 for Matte Finish). These guys supply Seat Heaters for practically everyone and I suspect they may for Porsche as well, but don't advertise it.
You might also need to get a pair of interlocking Relay Boxes (don't know if they're included in the kit), but the best source for these is Painless Wiring -
http://www.painlessperformance.com or WayTek Wire -
www.waytekwire.com/bosch-automotive-relays.htm . You can also use Molex Connectors to easily use the OEM Switches from -
http://www.molex.com/cgi-bin/bv/molex/jsp/contact/mxcontact.jsp?BV_SessionID=@@@@0920931359.11768748 64@@@@&BV_EngineID=cccgaddkjjhmifjcflgcehedffgdfmk.0&channel=Contact%20Us&channelId=-8863&pageTitle=Find%20a%20Distributor making it Plug & Play
There are several sources to pull the power from, both switched and unswitched and the wiring diagram is simple, though contrary to the Installation Guide, I would use Relays for the High Current to the heaters themselves and low current for the switches. See their Installation .pdf here -
http://www.heaterseats.com/installation.pdf
If you can install a Car Stereo, this Mod would pose no problem at all. In fact, it is easier than several of the Stereo installs I have done over the years. Hope this helps...