I asked myself very similar questions when I started photographing weddings (Started with a Nikon kit, but switched to shoot wedding with my Fujis).
But there are more aspects to cover in your decision.
A wedding differs from a normal shoot in the those aspects:
No, no, no tolerance for faults. Broken lens, broken body, broken sd card, broken whatever kills you.
No time to change lenses in critical situations --> Working with primes (which I personally prefer) means carrying around multiple bodies.
You'll need a wider length for covering context as well as the possibility to go very tight for portraits
So you definitely need some backup gear, whether a second body or a second system.
To answer your question: I solved those needs with an additional X100s camera including the tele and wide converter. This gives you great flexibility, even in low light for a relatively small price (if you consider to buy it used). Having your 18-135 attached on your right and a X100(s/t/f) on the left, TCL and WCL in a pocket would be my choice.
My personally most preferred setup for wedding stuff has been a 35mm 1.4 on a X-T1 combined with the X100s+WCL.
Hope this helps. Cheers, Philip