My vote: do that which achieves the result you desire.
I have done, and will continue to do, both, depending on my needs for a particular image.

If you do decide to do post work, yes, working large to start with is always a good idea, computer memory and processing capabilities allowing. Also, if you have Painter and use it for post-p, there is a way to record a low-res work session and have the program do the exact same thing in a higher res format. Check around on the web for info on print issues (hint: there's a print forum here at R'osity--you can ask print-specific questions there), and there are many many places that discuss other graphics apps (hint: R'osity forums...)
Hope this discussion topic helps...

RosemaryR
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"This...this is magnificent!"
"Oh, yeah. Ooooo. Aaaaah. That's how it starts.
Then, later, there's ...running. And....screaming."