If finances are an issue, I would skip out on the tripod for the wedding. I have never used one nor have I ever seen one used (my wife is half italian, so I have been to way too many weddings). Its just not practical. Pick a good spot outside for the group shots with good light, open shade. Don't worry about a tripod. You will have a fast shutter speed. If your shutter speed is too slow, people will be moving in the image and be blurry, and thats nothing a tripod can do to help.
As its your first wedding, first event shoot, you dont know your equipment, are renting a lens, using a flash for the first time... I'd also skip out on the diffuser and reflector. If I had to chose, get a reflector. If you dont have an assistant, look at getting a stand for the reflector (although husband as assistant can be fairly cheap

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The thing with the flash is that you can work in manual mode. You just have to take test shots to work out your settings. Again, hopefully with an assistant so you can practice on real people. But your best bet is a flash with TTL. While they are more expensive, it will help alot as the camera and flash will work together to establish what to do. You control camera settings and then the flash exposure compensation.
Do not get bogged down by your gear. Gear is important, but really, if you are focusing too much on getting new things and trying to use them, you wont have much time for the actual picture taking.
Focus on finding good places with good light to take the pictures. Again, open shaded areas outdoors work very well. Watch your background so that you dont have too much sky (which can make a blow out).
My first wedding I was also thinking gear overload. I kept it simple. I had a variety of lenses, had a 430EX II flash and thats it. No tripod, no diffuser / reflector...I was able to concentrate more on composition and making the B&G have fun and smile than where to place the reflector and what power setting to put the flash to.
Dont forget you will also be moving from one place to another. Pictures of them walking can be candid and nice as well. But if you have to run back to grab your gear, close it up, pick it up and move it, then drop it when you see a photo op, pick it up again... it just aint gonna work