Patience, Grasshopper!
YOU have the cash, YOU are calling the shots.
I don't care a whit about a 300 mile service. Oil change, filter, spark plug, pop the tank & pop the valve covers, look at the clearances with a feeler gauge
yourself. ONLY THEN will you know it was done.
Look on Cycletrader nationwide and see what the real availability for your favorite color scheme is.
Often a bus ride /field trip with a friend will tip the scale in your favor. Don't hesitate to look 250 - 500 miles out.
If the Fireball is actually available for $1500 under a new one, I'd learn to like it. If the owner is reluctant - move on. You have cash, if he really wanted to sell he'd do so.
These new 350s are very Japanese-like. I'd be amazed if they don't routinely run 50,000 to 75,000 miles with normal maintenance and under a sane rider. I wouldn't get too hung up on warrantee or worried about a machine with 5,000 on the clock. Chances are good you can find a nice used 3,500 mile on-the-clock "dresser" version of what you are after from some poor soul that suddenly feels he needs "more bike" because his
friends can run 100 MPH.
Be patient, look around, find "the deal", don't sweat the warrantee BS - it's a 350cc OHC single, not a Hayabusa. Warranty periods are set by the predicted mean time between failure, if they were going to lose money honoring the warranties, they would stop offering them. R.E. has built a lot of bikes, it's unlikely you'll have any engine issues.