I'd probably not carb right away if you have the ability and experience to force carb. Once you carb it up, the yeast won't be actively cleaning up and letting it age. I'd bulk age it in the keg if possible, then force carb it a few days before the wedding. The higher the gravity, the more beneficial this cleanup time would be. I probably wouldn't bother for a cream ale or hefeweizen...
Yes, you can store in the keg without carbing as long as you observe proper sanitation and then seat the lid. To do so, turn the stop valve on your regulator to off, crank up the pressure to about 30 PSI, then open the valve while pulling up on the lid in the unlatched position. Once you feel it seat down, turn the stop valve back to off, check for leaks with a spray bottle, and lower the pressure setting to around 5 PSI.
No, it's not possible to overpressurize a keg by carbing to long, so long as you don't pressurize it beyond the desired serving pressure and you don't chill it before serving temperature. If you'll be serving at 50F at the wedding, force carb it at that temperature at home.
Now bleed off almost all of the pressure using the relief valve on the keg lid, then refill to 5 PSI. You'll want to move the stop valve to the off position every time you burp the headspace, or you'll just be wasting CO2. Repeat this 5-6 times to get below 1% O2 in the headspace, then disconnect the keg and leave pressurized at 5 PSI. Double check for leaks before storing. A properly sanitized, sealed keg with 100% CO2 headspace will stay good for many months, even at room temperature.
Be sure you don't pressurize all your other kegs to 30 PSI accidentally. 
Really, the best answer would be to buy another fermenter. I know that's probably not what you wanted to hear, but I've never heard anybody complain about having too many fermenters or that they allow for too much time to bulk age. If you're married, you could write off the $15 for a bucket as part of your present to the bridge and groom.
