Don't do a white tux. Only .000001% of the world looks good in them.
Get a full vest. The ones that just attach in the back look stupid. Get a black coat, pants and black patterned vest. Ask to try on both a bowtie and a regular tie and see which you think looks best, although the regular tie is usually the better.
All in all, you'll want to get a rental from a place that has people that know what they are talking about... Mall stores like Skeffingtons might not always be the best. I've had good experience with Men's Warehouse, if you have one of those near you.
If your girl has her dress already, take her to a craft shop and get some ribbon that matches her dress, various widths and stuff, and when you go to order your corsages, give it to them to add in. That's all the more color matching you need.