Well what you say is true to a point Dave ,I'd change the old oil , I'd first turn the bike over a few times with the old oil using the starter motor and the sparkplug wire off to be sure the filter is full ,before draining , change the oil but leave the old filter in place until the bike runs the first time , that would allow 75% of the oil to be fresh at startup ,rather than !00% questionable. Even new oil can be ruined if not stored in a place where temperature remains stable ,I'd be leery of the condition of oil, and condensation  that might be trapped   in the bike ,that sat for 6 years.

Letting it run (idle) for 5 min, may not warm the motor /oil , and may not be good for it, your not putting any load on the motor. I would go ahead and change the oil at this point ,but then ride it around the block a few times ( if it dies for any reason you can push it back home),leaving the choke on as needed (until you can push it in ). You won't know if the fuel flow /carb needs attention/ clutch slips /brakes works / etc. until you actually Ride it! I wouldn't change the plug at this time ,the sparkplug in it now is working ,  and a new plug won't change anything   . I'd save the new plug until your sure the carb /petcock is working correctly. If the fuel flow from the petcock is slow you'll know when you ride the bike as it will limit your speed or the bike will die /or falter as you try opening the throttle more. You could at that point check the tank for rust, pull the petcock and clean the filter screen, or clean the the carb. ( if you need to clean the carb ,come back to us and we can walk you through it , there are some do's and don'ts you'll need to know so you don't damage it.)

See if theres a drain bolt or plug, underneath the float bowl, you could take this out and see if any crap drains out, make sure there's not much gas in the tank if you do this.