Welcome to the forum and congrats on your new to you camper. A few words about your "like new" trailer, especially if it's your first. Some things that don't wear out but can cause issues if not maintained.
ROOF, WINDOWS & DOORS - it's crucial that the roof seams and penitrations are sealed. Check the cualing/sealant for any cracking or peeling. Check the sealant and gaskets on all exterior penetrations for signs of water intrusion. Water is the cancer of RVs, it will destroy them from the inside.
TIRES/ RUNNING GEAR - .if the tires are original he trailer tires most likely will need to be replaced, even if they have zero miles on them. ST (special trailer) tires age out before they wear out. Most folks replace tires at year 5 or 6 from the date of mnf which is molded into the sidewall. The OEM tires may be marginal from day one as Keystone doesn't use the highest quality brands. Check the brakes for operation. Setting for years the brake components may have rusted to the point of not operating. Inspect the brake wires, some small rodents may have damaged the electric brake line wires. The wheel bearings should be inspected and repaked.
BATTERY - if it's original it's going to likely be toast, especially if it wasn't keept an a battery maintainer.
WATER SYSTEMS - If the trailer sat unused then was it properly winterized? At a minimum the fresh water tank and system will need to be sanitized. Fill the FW tank, turn on the pump and bleed the air from all of the water fixtures. Listen for the water pump NOT start running unless you open a faucet. If the pump starts up with all faucets closed then there's a water leak.
APPLIANCES - check for operation of all appliances including the furnace, air conditioner, water heater, etc.
ODORS - note any "musty" or "moldy" smells inside. Let your nose be the investigative tool, in cabinets, under sinks, etc. If there's a moldy smell that's indicating the presence of mold which indicates water intrusion.
This list is not comprehensive. The intent is not to discourage or dampen your enthusiasm but rather to inform. There's nothing worse than purchasing a major item just to find out that you may need to spend hundreds if not thousands of dollars afterwards just to make it usable. Good luck with your new venture. I hope you have many wonderful days & nights ahead making new memories.