Regarding manual focus, make sure your focus confirmation is correct by making some tests - but you're going to stop down (I suggest f4 for both the 50 and the 135) so the focus should be fine. With the 135 you can even go f5.6 or even f8 and still get great separation from your background.
People said don't use your onboard flash - but if you're using a longer lens like the 135 you can still use it for a slight fill that can help the shot. I use the onboard flash for daylight pictures if I'm against a stronger backlight and i want to preserve the background colors somehow.
At the end when you know you already have the shots you need, you can let your hair down so to speak and get the lenses wide open or almost there, and just shoot some more. If you get a keeper great, if not you already have other more "conservative" shots - that will still be better than your 50-200 anyway, because you'll have to shoot that one at least at f5.6 to get ok results, and it still won't be as good as the primes.
Summary: take the primes, stop them down to f4 or f5.6 to get the shots you need. After that, experiment and have fun!
Good luck and hopefully your friend will let you post a couple of pictures here for us to see