The advice I got was to buy used because RV's are built, not manufactured, and usually have punch list of fixes that show up in the first year. Obviously used units also depreciate more slowly.
In terms of repairs/parts there are repairs to the vehicle and repairs to the RV. With RV repairs the current shortage seems to be skilled mechanics rather than parts. Getting quick service can be very difficult regardless of parts availability.
Choosing a unit that reduces the likelihood of need for repairs. For instance, getting an all-electric unit eliminates the propane system. One less thing to go wrong. AGM batteries are a simpler technology than lithium which require a battery management system.
With the Mercedes Sprinter chassis there may be problems finding someone to work on it in remote areas for some of the high tech components. But we have put almost 50,000 miles on ours the last two years with no breakdowns or mechanical repairs beyond standard maintenance. Diesels also hold their resale value better and get better mileage. I assume you are not one of those people who drives from a store on one end of the parking lot to a store on the other end. If you are, I would avoid diesel since they are not known for liking that kind of use for multiple short trips. They seem to have many fewer problems when they are only started and driven a handful of times a day.
Since you are planning to spend a lot of time driving, I would suggest you focus on the comfort as a vehicle. The front seat is going to be your living room a lot of the time. So consider the view it gives while driving as well. Almost any B of proper size will give you the basics you require but an upscale chassis like the sprinter is going to be a lot more pleasant while in motion.
Think through the process of stopping and what you will need to do to set up each night. We can stop and get into bed with no further thought. Get a unit that charges the batteries while you drive and provides enough battery storage to get you through a day without recharging. Solar panels add complexity, but they can provide enough juice to keep your basic systems running indefinitely while you are parked somewhere without any shore power.