Art- while I know that the USD is stronger than the Can$, $1000 Cdn seems a bit steep for prints in your first ever exhibition, especially at a cafe. You would know your local market better than I, so maybe that's the going rate for art in a cafe. I'm donating some work to a local AIDS charity auction, and pricing it at $400 for the auction night itself. This is an 8x10 Palladium print, mounted and framed to 16x20. I'm donating the rest of the edition to them on a 50/50 split, for whatever the print sells for at the auction.
I'd be wary of the charity donation if you do not have explicit support from the United Way chapter, as it doesn't usually increase sales. It may help your customers feel better about the purchase, but it won't by itself get someone who is fence-sitting to buy something they weren't already going to buy. It usually works better the other way round... "Oh, if I donate another $100 Cdn to the United Way, I also get this cool photo, and not just a receipt and a thank-you form letter. "
As to the exhibition, while you can mix different types of prints, you are more likely to be successful if you exhibit one thing consistently- all b/w fiber prints, or all color, or all scala/ilfochrome. What is on the wall and highlighted should be consistent. Bring baskets of matted but unframed stuff along to sell in addition, and the baskets can be totally mixed. IF your budget for the show can handle it, I'd take your matts up to 14x17, to give you a nice, bigger white space around your images to separate them from the brick wall, ESPECIALLY if you are exhibiting color. The red brick will automatically influence the color perception of the prints on the wall, especially since you are hanging in mixed lighting.
Postcards - more is better. Especially since more costs very little more than less does. Get at least 1000 cards made. You can then leave stacks of them at the cafe for people to take home. Most cafe/restaurant/bookstore buyers don't buy on impulse... they see the work, they go home, think about it, and come back. You'll be more likely to get follow-up sales after the show closes if customers can take home a postcard. Also, you can give the cafe a fat stack to mail out - I'm sure the cafe owner has his own mailing list. You might even be able to get him to pay for part of the printing (hint hint!).
The artist bio and statement about the work is nice, but not required. I've done a little blurb to put up next to my work, and framed it in a cheap MCS plastic "invisible" frame so it will hang alongside the work and be there to speak for me when I'm not. It is a good way to post your prices and contact information, especially if the cafe has run out of your postcards and you haven't been by to restock yet (remember this point!).