Do a search. Search is very powerful. If you searched on "C280 seats" you would find this thread:

http://www.peachparts.com/shopforum/showthread.php?t=132934&highlight=c280+seats

That thread answers the seat problem. As far as windows, they are all on the CAN bus like MB DOC said. I never heard of them all failing at once. I did not know that relay had to do with the windows also. It is worth a try. You can try fixing it as explained in the other thread or just buy it.

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1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra