I like hoods on Jackson. Things without hoods always seem to fit him awkward.
D-ring attachment on the jacket itself is not a big deal to me but I DO like to have a slot where his harness can pull through. If there's no slot, a d-ring would be helpful.
I'm iffy on sleeves. I personally don't like them as much because it makes them more difficult to get on and they seem less comfortable for Jackson to walk in.
Velcro I tend to like better. It just seems easier. I have a jacket with buttons and it is harder to put on.
As for the belly, I don't really care either way.
And yay I hope you do start carrying some. I don't need any now but am always looking for good jackets and hoodies in the fall/winter. I don't have a raincoat for him yet either.