Second body? I'd not bother with the TC (not that I shoot weddings).
It ultimately depends on your style but as a Canon shooter people generally use the 17-55 f/2.8 or 24-70 f/2.8L as their work horses depending on FF or crop. Whilst others choose to shoot with two primes like the 35L + 85L.
But don't rule out ultra wide.. love this guys work, not sure he even uses flash much but does a lot of great stuff with a 14-24 f/2.8 on full frame..
http://www.pbase.com/eminilia/wedding
I'd personally go for a 17-55 f/2.8 + long prime like the 85 f/1.8 or 100 f/2 for low light church shots and candids, think an external flash would be invaluable.
p.s. POTN wedding section is worth dropping into..
http://photography-on-the.net/forum/forumdisplay.php?f=78