I was in the easier position of living fairly close to my Mistress, and most of our friends knowing that we're kinky, but here's a couple of thoughts.
Think about the collar, what you want, what she wants, and what you can get away with for everyday wear. Mistress bought me a nice, simple metal ring collar that fastens with a hex screw (allen wrench). For a while I was able to wear that constantly, but when I had to go back to a 'normal' job, we agreed that I would wear a ring instead, and keep the collar for when I was on holiday. (this looked like being a bit awkward when I got married, but my wonderful wife agreed I could keep the same ring as my wedding ring).
Next, outfits - think wedding :), but your outfit also has to fit what your Mistress wants you in. I was in a rather goth gold and black outfit, because we both like me in that sort of thing.
Ceremony depends totally on how the two of you want to do it. You will both want to come up with vows that set out how you feel for each other, and what you bring to the relationship, and things like that.
Witnesses could be a bit tricky if you don't have kinky friends.