I recommend going to Klaus' meat market and picking up a variety of authentic German sausages. Try some fresh and some smoked. Easy to cook and will definitely please the crowd.
If you can't find brown mustard seeds, just do all yellow. Brown is hard to find (for me anyways).
And if you do make your own, they say to grind the seeds after soaking. You don't need to grind them till smooth; you can leave some "chunky" as they are still going to be soft. Just gives it a bit of texture.