The factory wax should get you through most of the first day depending on the snow conditions. Colder snow will pull the wax off quicker than soft, wet snow.
The more wax you push into your board, the longer the wax will last and the more protected your base is. Some will argue with me, but you can never wax your board too much.
If you use an all-temperature wax, I'd wax/scrape/brush a couple of times before heading out.
If you use temperature-specific waxes, I'd push a couple of layers of warm wax first, and then whatever temperature wax the conditions call for on top of that. The idea is that the warm wax will sink in further into the base and create a foundation for the colder waxes to bond to.
Whichever route you go, waxing your own board is easier and far cheaper than using a shop.