good questions!!
the double vent comes with newer models now standard. Its just a new vent system that can be purchased for older cookers. Dennis told me that it really isn't that big of a deal either way so I wouldn't worry about that.
Gas port has a door at the back to insert it. I wanted mine removed from the 23s, so I had a new one cast. Dennis recommended me keeping it on the 32" for two reasons. Winter cooks I can pre heat with gas.. and more importantly I can remove that cover for cold smoking (better air flow). So I think keeping it is a good call.
the probe hole has rubber plugs that seal it up when not in use. Your KK kit will have 5 extras apparently as well.
I think personally for accessories
rotisserie
baking stone
splitter basket (with extra basket optional. I think having a primary charcoal basket for the splitter to sit in is a great idea)
Side tables if free standing
double lined drip pan (custom fit)
as for the 23 or 32 I have nothing to compare to, however, I am thinking the 32 is pretty sweet!! But in the case, I really don't think that you can go wrong with either... or in my case... Both!!!