Boarding is different from check in - everyone can check in whenever as those times are not really enforced anymore at most ports. If everyone shows up after boarding has started (sometime after 10AM), you can board together. Everyone will be on board by lunch time.
Smoking is limited to the usual locations. You can view Spectrum related threads, which should have a review of something like you will encounter, via the drop-down menu on the main page here at RCI section of CC.
It's likely a temporary issue. You can try a different device/browser to see if you can duplicate the issue. The price w/grats included has been reported by others in a different thread.
It seems RCI is trying to confuse things by not making it obvious that they likely mean an E and D category GTY instead of the generic XB GTY. I would still be weary of picking any non-category specific GTY if you really want to stay away from E cabins. Not sure that even an RCI CSR call will eliminate that possibility.
Unless it's a specific category GTY (like 4D) don't pay anything extra for any other balcony GTY. That may even be an IT glitch as Q class don't usually have more than one general balcony GTY.
Welcome to CC.
That may depend on the cabin but it's probably pullmans for guest 3 and 4. Look on a site like cruidedeckplans on any Radiance class ship for your or similar cabin for layout.