What you need to know is what the total wattage of the "clothes" will be, and add that into the full running draw the bike has all lit up. Most of the small scooters have a 35 amp alternator/stator with 65 amp peak, and really are already hitting the limit.
A larger ah battery is a good idea if it fits. It is nothing more than insurance tho, and will not effect how much power the stator puts out.
The biggest draw on the bike is always the blinkers followed by the head/tail light. If you replace the blinkers, and other lights w/ LED's you will gain back almost 25 amps. A full conversion is generally around 25-30 bucks.
Good luck, and stay warm.