Great lens for $300 used. Do it.
I have two fast autofocus primes. The EF 85 F1.8 (lighting fast, small, sharp, F1.8). And the EF 200 F2.8L (lighting fast, light weight for 200 F2.8, black, sharp wide open, F2.8). Inexpensive. I paid more for my 85! I caught my 200 on a slick deal.
I use my 85 F1.4 more than my 85 F1.8, but I use that 85 F1.8 for things where I want focus speed. I'm pretty fast with my 85 F1.4 (manual focus), but the 85 F1.8's speed is so fast that sometimes it's just the right tool. Like when I shoot kids soccer, I love that lens, it keeps up with running kids. So it should be fast enough for a slow wedding.
The other beauty is, the wider the aperture, the more light it can grab for autofocus purposes, even if you're stopping down to F4...