Think a planet only thing would be very niche (IE it won't appeal to such a broad range), it will also likely need to be large for mostly the aperture which provides the resolution, and the focal length which comes with larger aperture, so don't expect it to be cheap.
Regarding required focal length, I've imaged Jupiter and Saturn at around 700mm using a 2x barlow lens, and have also viewed with the same, it was okay and very sharp due to using an apo refractor. I've also imaged and viewed at 3000mm, but such a thing requires more investment in pretty much all your equipment (IE another rig), then atmospheric seeing also becomes more of an issue.
