For an outdoor wedding, it sounds like you should be crossing the golden hour near the end, but still have strong light. The bigger trick will be the angle at which the sun goes down. You will want to shoot with the sun behind you if at all possible.

The fact that the wedding is outdoors is actually advantageous to your cheaper camera as light levels inside for a wedding are often far, FAR lower than an outdoor wedding. You may not even need the flash at all, though if you do need it for fill, use the reflector to provide a more diffused light source unless it is not powerful enough to give the fill you need (in which case you will need to switch to direct lighting.)

I'd also recommend going with the zoom lens until you can no longer get the exposures you need. While primes are great for portraits and fixed shots where you have time to get everything just right, they are a major pain to work with in a wedding where you are a secondary concern and you don't have time to fine tune everything and have to work on the fly.

I usually shoot aperture mode for weddings to give me direct creative control over depth of field, but I also monitor the shutter speed and ISO closely to make sure they stay in range for what my camera is capable of doing well. Granted, I also shoot on a 5D Mark iii, so I have a much wider array of usable ISOs than you will have, but you are also outside which should provide you far more light than I normally have for interior weddings, so you should probably still have some ability to adjust ISO to get wider depths of field for shots where that is advantageous.

Also, since you don't have to worry about high levels of action in a wedding, there isn't much sense in using shutter priority, though shutter priority can be handy if you are taking photos of things like the bouquet and garter tosses where you want to be able to catch it in mid-air.

Another practical, but important piece of advice is to remember that you are trying to capture the event, not be the event, so do what you can to avoid being a distraction. In your case, it sounds like you will be seated in a front row so it doesn't sound like you'll be moving in front of people or anything, but also be conscious of the shutter noise and flash (if you are using it) from your camera. Sorry if that seems obvious, but there are even many professionals who seem to forget that simple fact and end up being a serious distraction during the service.

Using mirror lockup and shooting from the LiveView can help reduce noise some if you don't have a quiet shutter mode on your camera, though it will decrease the speed of auto-focus unless you have one of the new hybrid AF systems in your camera. However, since you are outside, it may be difficult to use the LCD since it is bright (and the noise will also likely be less of a problem as there aren't walls to bounce off of and there are other outdoor sounds going on.)

Just try to stay aware of the situation and avoid causing unnecessary distractions to people. Watch for other people trying to take photos and try to stay out of the way when you can and balance it with your need to be able to take photos. Also, it doesn't hurt to check with your friend about any guidelines they'd like to have followed (such as use of flash and what not). Often, the response is to use your judgement, but it doesn't hurt to ask.