You certainly have some skill, I'm not as worried after seeing your photos. The key is preparation, making sure you know how you are going to get each shot. I used the wedding rehearsal to practice, asking them to walk through the wedding as much as possible while I take shots. Plan out where you are going to be, what settings you are going to use, etc. Don't be afraid to use program mode if everything falls apart, but
Here is what can happen. You prepare, have everything lined up in your head, and then the big day comes. You forgot you put the aperture at 11 in order to get the shot of the rings in a flower or on a shoe, and all of a sudden you are shooting the wedding itself. All the photos are blurry because of the slow shutter speed, and you didn't notice like you usually would because everything moves so fast you never had a chance to check the screen to see what you were getting. It's not lack of skill that kills the amateur wedding photographer, it's lack of routine. It moves so fast and you can't slow it down or figure out your setting on the fly. You just have to know it and do it.
I taped a reminder on the back of my hand to check aperture frequently since I was shooting in aperture select mode. You need to be able to focus on the wedding and composition, not settings. For you it could be a different thing, you just need to know your weakness and defend it. Make sure you make a shot list of things to get, you won't remember them otherwise. Also find out ahead of time if they want family group shots and who all should be in them and when/where that will take place. You don't want to figure any of that out the day of the wedding, and you want to keep them as simple as possible. Outside in shade with fill flash is perfect.
The T2i would work, the idea of renting a 5D isn't bad, but comes with risks. You wouldn't know the camera and might screw things up in some way you can't predict. But on the other hand you could set a nice high ISO, use a smaller aperture to avoid focus problems, shoot faster shots to hopefully get more winners, etc. The zoom would be great because shooting a wedding with primes is tough enough with experience. If you shoot with primes I wouldn't plan on changing them out much.
Make sure you have a good talk with your friend. Tell him it's possible you will do something (like the above example) that will result in missing a big chunk of the photos. You can do your best, but you aren't a professional and weddings are fast paced and not repeatable. Ask him how he would feel if the above happened and to think about it. If he still wants you to do it, I'd go for it. It's very stressful, but also fun to put such a big challenge in front of yourself. I asked another guy at the wedding to be my "second shooter" and get as many of the key moments as possible for backup. Thankfully mine turned out because he didn't get a single decent shot... :)
Oh, and your percentage of keepers is about the same as mine, and held through for the wedding also. I shot about 1800 (preparation through reception, constantly looking for those little shots like grandma's tears, kids watching the bride, dad looking on proudly, etc) and gave them about 160. Don't give them everything, they won't care in 10 years when they look back on the photos, they just want to see the best shots and highlights.