haha...he may "hate posing for pictures"....but my guess is that the parents and/or grandparents have yet to hear about a lack of posed portraits.....they tend to like those.
I would get to know the venue a little bit. For Squidy, he is in a park. Will you be in a church? Restaurant? What is the lighting like? Is it day or night?
Considering your personal aspirations, I would make sure you can do a competent job, but I am not sure I would start building a classic "wedding photographer" kit just for this event. For example, a pair of the better professional wedding photographers I've seen worked almost the entire wedding each shooting with 5DIIIs and a EF 50 f/1.4. They simply "zoomed with their feet" and got some great images. So, that would be equivalent to your cropped sensor and 35 f/2 IS.
The first wedding I took photos at after getting a dSLR was my sisters. Turned out she hated the pro's pics, and her wedding album is mostly my shots. Back then, 7D EFS 15-85. Almost all shots were f/5.6.
My wife's Uncle is a pro who used to do a lot of weddings (massive dislike of them now, mostly does corporate/schools/senior pics/etc). I've talked with him and he almost always locks in at f/5.6. Liked the deeper DoF so that he is less likely to miss a shot/moment. Only went to a faster aperture at times when he felt he was more in control of the scene (portraits).
My point being that while there are a couple of ideas of gear you need for weddings (f/2.8 zooms, or even faster primes). You can and people do shoot weddings with other gear. In this amateur's opinion, the most important things about weddings is documenting the people, event and capturing the key moments. It is often an uncontrolled situation. But, it is still "just" photography. The biggest difference I have seen between pros that I thought were good and those that weren't at weddings was a willingness to work (get angles, get into position) and to interact a little bit with the people (ask groups to pose, go around to each table at a reception and photograph that table, etc).
So, in terms of your gear, unless you want some gear for another purpose, I would say you need a flash, I have never owned the 430 but am tempted to get the RT version and hear it is good. I known and understand a backup body is important for a pro. But this seems more casual and you have a backup photographer. As it is you spending your own money, I would only purchase a second body if you want one. If your friend is "counting" on you for the shots, then you might consider renting a second body for this event and making this part of your wedding gift.
Other than that, I would try to get an idea about the location. Work with your friend and his fiancé to see what shots they want. Wait to see if posed shots come back around.