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The best sandwich I think I've ever made was on focaccia. I grilled thin slices of zucchini, put them on with tomatoes, roasted red peppers, marinated eggplant, provolone and fresh basil. Also made a basil vinaigrette to put on the bread then closed up the sandwich and grilled it between my cast iron pans.

Took them on a picnic to watch some fireworks, damn those were good.

Ok, this kinda turned into a long post but I really am passionate about this stuff.

Starting with what's most important and it's been said but really, make sure you get coffee that is not only good but stands out. Ensure all your service staff understand how important coffee is to brunch, it often makes or breaks a tip for me. If you aren't on the ball with refilling the cup, it will usually cost you. Nothing dampers a meal more than repeatedly going to take a sip of coffee from an empty mug for half or even a quarter of your meal. This does apply to any meal but is especially important for brunch. For a type of coffee I'd recommend finding a unique local roaster to get your coffee from. Advertise the fact that you get it from them and it really doesn't hurt to have more than "regular" and "decaf". Some of you may scoff, but coffee is comparable to wine and should be treated in some regards similar. If you treat it with even a third of the regard you give wine, people will take notice. Noteworthy is that good decaf always costs more than good regular, if it doesn't you gotta hope your supplier is taking the hit because often the cost of extra processing results in using inferior beans and since the processing detracts flavor, decaf lovers will be left in the shadows. Although, seriously, I wouldn't bother with decaf but would offer decaf americanos for the same value. I might be underestimating how much decaf is served but it seems better to take the hit on giving free refills for the decaf americanos than having a decaf pot that gets stagnant and disgusting, souring the decaf drinker's entire meal because he keeps taking sips of bitter or burnt tasting decaf coffee. Of course, having a fine selection of espresso drinks will go a long way, people love those things. (Still a black coffee man)

Something else is make your own petite croissants fresh for people and serve them hot. Maybe with a little compound butter or preserves. A place by my house does that and I love it. It's such a great start to a nice brunch.

As for french toast, make it like no where else. People will tell you to gussy it up with flavorings and such but try this. Cut all your bread for the next day the day before and leave it out to go stale. Make the egg mixture the night before and let it sit overnight in the fridge too. Soak the bread for at least a half minute or so a side, let that sit, fry it till golden brown, bake in the over at like 350 or something for 10 to 15. Trust me, it beats the pants off of any fresh bread french toast I've ever had. I can't order french toasts in restaurants anymore because I started doing it this way. I started with the recipe from Good Eats and went from there. If you don't get what I mean, watch the episode Modern Toast and give it a whirl. You'll never go back, I guarantee.

Another thing I find is never done right, hollandaise. It's SUPPOSED to have lemon in it. Over 80% of eggs benedict I've had give me more a bechemel or bearnaise. Just having a nice lemony hollandaise with the traditional ham and English muffin goes a long way. I do like a lot of the fancy ones, especially if you incorporate the caviar mentioned earlier. Delicious.

Don't underestimate the importance of simple choices on stuff like breads and jams. Getting high quality jam or marmalade for your toast (preferably made by your restaurant both bread and preserves). Make sure you have sourdough at the very least. Brunch is a lot of getting all the little things right and innovation.

I know I just keep going but I'm really passionate about brunch and can never find a place that really fills my needs or expectations.
Having set dishes that are unique is great when they are things people won't think of putting together themselves but if you are flexible in your more basic breakfast like the hashbrowns, eggs, bacon, sausage and toast collection of breakfasts it will make a lot of people happy. Being able to add, exchange or take away things for a sensible cost goes a long way. I mean a really long way, most places charge about 4 bucks just for a few more sausages, or to add bacon. Some places won't let you interchange the two, or mix and match.

Lastly, I agree on not going with any kind of dim sum fusion thing. If people want dim sum, they will go out for dim sum. You want to bring in the brunch crowd. A topper on all this, I love a good not overpriced mimosa. One place that forevers tops my list for brunch did the croissant thing I mentioned, does dishes a'la carte and has $2 mimosas. Classy atmosphere to boot. It's the closest to what I've always wanted in a brunch place except they don't have great sausages.

These are just the suggestions of a man that loves food and is especially fond of brunch, the meal and the concept. A meal that should be spent in leisure and good company.
Again, I apologize for the length, I hope things go awesome and I'd love to hear how things turn out.