most flashes will have a bounce card built in so they will look the business.
Try to get used to handling a big camera, big lens and big flash combo as you will be grateful for it by the end of the evening. Most of the weight should be on your left hand with the right hand really only offering balance. If you don’t do this your wrists will hurt. You need to be holding on to the lens though instead of the flash as how else are you going to work the lens? With the lens in portrait position I generally angle it to bounce off the ceiling however if you can bounce off walls that generally gives a better quality of light as it comes from the side.
Don’t worry about the yongnuo flashes, they are good things and while they probably aren’t as reliable as the canikon equivalent you can fit three in your bag and still have money left over for batteries (sanyo eneloops is my suggestion). I have several YN flashes myself. A TTL flash for events is a much better idea though and never forget you very rarely want it pointing straight at people.
Good luck, it sounds like you have an excellent friend to help you out with this