There really isn't a rule of thumb on how old of a Newell coach someone should buy. I would say it depends on your needs and budget. If you want an older vintage Newell you can find them but they will most likely need a lot of fixin.
If you are wanting a project you will find one. However there are older ones that have already had updates and redos and have been well maintained. If you want one ready to go and with less things to fix a newer coach maybe the better route. Have you checked the
NewellClassifieds.com ? Once you have an idea of a budget and your needs from a coach then you can narrow it down.