All hard to say dude, if you drink a lot of coffee and smoke then wait until you've got 3-4 weeks before your wedding day, then start treatment. If you don't drink coffee a lot and smoke then wait 4-7 weeks before.
As far as the gums thing, it's all dependant on the person really, and what condition your gums are already in.
It won't happen if you avoid putting the strips over your actual gumline, and depending on how far your gums are receeding from your teeth shouldn't affect how they look overall.
Then again if your gums are receeding really far, you'll have discolored areas where you didn't cover your teeth to avoid bleaching your gums out.