It wouldn't be insane to try growing pots of tuberous begonias but it might make you insane or put undue stress on you by fretting over them. You could try it but you should have a backup plan in place - maybe if they don't look too good a couple of weeks before the big day, you should contact your florist to see if they can help you out.

If you get the bulbs now in the colors you want and cater to them until the event, they might surprise you. They can also take a nose dive as well. eBay has some good looking ones for sale now as well as garden catalogs and local nurseries should be gearing up.

I don't know much about Wisconsin other than my sister and her family lived there for about 5 years and enjoyed it.

I'm not a tuberous grower but the ones I've seen (and grown) seem to bloom in flushes (lots of blooms at one time, then a few here and there, and then bloom heavy again). Non-stop begonias are supposed to bloom all the time but the blooms are smaller. Insect problems are minimal with begonias but you should still keep an eye on them to keep problems at bay. The worst problem is sudden collapse either from drying out or too much water.

You could probably get blooming ones from a garden center but spring is the best time to buy - I'm not sure if they would be available in August for your area. When my sister lived in North Dakota and we visited in August it seemed all the garden centers were closed for the year (ugh - I don't think I could handle that).

I think I would work backwards and see what's in bloom in August and is plentiful. I wanted orange blossoms at my wedding in June and of course orange blossoms are spring time bloomers so that didn't work out.
I made the centerpieces for my daughters wedding and although the guests were civilized, everyone took the baskets like they were hotcakes. Believe me I'm not that good at floral design. So if you planned on using these plants in your garden, you might want to rethink that.
Congratulations and I hope your wedding is everything you dreamed.
Barb

Maybe not insane, but risky-I would talk to your local garden center & see what they could get you at that time, that you could plant in your garden afterwards or give to your guests to plant. We were married in Oct., in Charleston, went to a garden center, bought lots of lavender crysanthemums (not my favorite plant), plopped them in containers & told everyone to take what they liked afterwards-this was a 'destination' wedding, we lived about 3 hours away, as did most of our guests. It turned out great, remember, as much as you love plants, this is just a small part of your wedding-don't stress over it-figure out what's going to be easy...