Class B RV’s

Cool plan and awesome you can doo this!

However sounds like you’re looking more for basic financial advice than RV advice. 
The RV market, just like the housing market in some areas is still in the tail end of “Coviditis” decisions. 
Not to mention the “#vanlife” crowd that I think is not as prevalent as it was a few years ago. 
If you’re looking at used coved era rigs, most probably overpaid and/or are upside down if there’s a note on it. 
You’re headed the right direction. 
Know what you can get a new one for bottom line and then use that to negotiate used prices. You’ll weed out the upside down dreamers from the realists and end up with a fair value on a used one likely. 
Financing? Just do your homework and if you can’t, have someone do it for you. Or since you have cash, ummm, you kinda answered your own question unless your a savvy investor. 
New vs used?

I would NEVER take a brand new RV and just hit the road long term. RVs notoriously have more “issues” that you’d rather warranty than fix yourself or possibly put it out of commission for a period of time. Not a great thought 2000 miles from home with 10 months to go and nowhere to stay without coughing up for a hotel or air bnb and a rental car. 
something gently used for a few years typically has those issues worked out yet new enough to be as “reliable” as new. 
JMO

usaly the older it is, the less the loss when you go to sell it.  some times if you are a handy person you could buy a vintage one, put a little bit into it and make some money when you sell it, but that take having the time knowhow and tools to do it.  

It sounds like you have a solid approach by weighing new versus used for minimal depreciation. Often, lightly used Class B’s can offer the best balance, but deep discounts on new models can make them surprisingly competitive. Financing can make sense if rates are low, but paying cash avoids interest and simplifies resale.