1st wedding shoot

I have been asked by a very good friend to photograph their wedding in 2015 at Marwell Zoo in Hampshire.
Now I have been to Marwell hundreds of times so I know the layout very well, but as this is my first time photographing a wedding, I was wondering if anyone could give me some advice about settings, Lens etc.
I currently own a Canon EOS 7D, Sigma 150-500mm f5-6.3 APO DG OS HSM lens and a Canon EF-S 18-135mm f/3.5-5.6 IS STM lens. I have access to a Canon EOS 1000D with the 2 kit lenses which were the 18-55mm and the 70-300mm.
Thankyou.

Since nobody has responded to this post I'll chime in. First off, your camera and lenses aren't nearly as important as your ability/desire to shoot a wedding. Perhaps you could seek out wedding photographers in your area and see if you could 2nd shoot for them in 2014? Equipment isn't necessarily a prerequisite to getting great images (if I were to spend a thousand dollars on tools, there's still no way I'd be able to fix your car as well as a trained mechanic could do). Also, the lack of a flash (or multiple flashes) seems a glaring omission.
As for what settings to use, there is no formula. The settings you use should depend on the available light (both ambient and whatever other lighting you have available to you), as well as the look you are trying to achieve. Shooting people in a rapid, ever-changing scenario (such as a wedding), with multiple lighting and time constraints, should be second nature before you attempt to solo shoot an actual wedding. This is why 2nd shooting is so invaluable, if possible. If that's not an option, do your best to go out and shoot your friends, girlfriend, whomever, as often as you can before the 2015 wedding. If your friends realize you have no experience, and aren't going to pay you, that's one thing. If they're paying you it'd be better if you had some real-world experience shooting weddings first.

In terms of gear: You need at least one faster lens, e.g. a 50 1.8. You also should have 2 external flashes--even if the wedding is taking place outside.

If you think you need advice about settings, turn down the job.

There's a longer answer but I can't be arsed.

You should start with knowledge, then worry about gear later.

Spend the rest of 2014 watching videos (like this) and try to second-shoot for an established wedding photographer.

Wedding shooters act as if their work is exceptionally tough and demanding. I think they are exactly right. Unless both the good friend and prospective spouse were exceptionally undemanding this experienced shooter would back away.

(It's true that some wedding photographers provide such junk that either you or I could do well in comparison. With some attention we could likely rise to the level of fully mediocre, but we both would want better than that for a really good friend.)

Agree with the above. You should suggest they hire a professional and you can probably shoot alongside (but not in the way) so you may get to grips with how weddings go. If you can't shoot alongside, just attend it like a guest but pay particular attention to the photographer and if ever, his shots at the end of the day (usually if there's a slideshow at the reception, you can see the photos right away).