Congratulations Brian on your 178. Be prepared to make a lot of great memories as you travel across this blessed land.
1) Do disconnect your batteries when not using for a few days or more as there are parasitic draws that will drain your batteries over time. This is a good time to purchase a multimeter/voltmeter. If you have 12v batteries than you want to read at least 12.72v from each or from a pair of 6v when they at rest and not plugged in to either solar or 120 shore power. Your 178 probably doesn't have solar built in unless the previous owner added it. We don't have solar on our 177 so while i cannot give advice there are many on this forum who will give you expert advice on this. Hold on, this is your 2/7 owners manual. Currently I have a pair of 12v Interstate group size 24 deep cycle batteries that will power me for 6 days when temps are in the 40's (furnace runs a lot during this time) as well as running both fridge and HW on propane. Do not run batteries below 60% S.O.C. or 12.2v before recharging, the onboard converter on the 178 will do that as you travel down the road with the 7 pin Bargman plug hooked up.
2) Being it is your first camper I would recommend you take it to a dealer to have it looked at OR have the previous owner you are purchasing it from go over it with you, that would be ideal and at the same time record it on your phone as you will receive information overload and will be able to reference all the info at a later time as needed.
3) Check tire pressure if Load Range C then 50psi (cold), if Load Range D then 65 psi. Look at manuafacturing date on the tires, strongly recommend replacing if older than 5 years. Depending on tow vehicle you may wish to utilize either a friction bar (anti-sway bar) or wdh for safer handling. Check to make sure everything works BEFORE leaving: outside as well as interior lights, furnace, HW heater-make sure tank is full of water before testing on both 120 and propane, have person you are getting 178 from show you how to access the winterization valves (2 or 3) under the queen bed at rear of the camper, stove burners, A/C, water for sinks, showers, toilet, check microwave, Dometic fridge, check to see it will function on 120 (after on - wait 5 minutes and place your hand on the heat stack on the back side of the fridge- it should feel warm or you should feel some heat coming out of the chimney at the top of the stack, after that turn on propane and go to the lower back of the fridge (remove lower vent outside) and look to see and hear the ignitor as well as see a small blue flame in the combustion chamber area. Get a good stepladder and look to see on top how well all the dicor sealent and caulk is looking around the ff fan, a/c unit, and 2" vent stack as well as the antenna. Run you slide in and out a couple times as well to make certain it is fully functional.
Any other questions that come up, please ask. All of us on this forum were once in your shoes asking the same questions.

Enjoy your new toy.