Dextrose is another term for corn sugar. I use it as it has a neutral effect on the final flavor of your beer. It is the the standard for bottle carbing unless you are going for a unique flavor.
If you have unfermented sugars then you won't be able to carbonate it in the bottle by adding dextrose. That high of a starting OG will leave a high enough FG. Pitch 2 packs.
I would pitch 2 packs of s05 in order to not underpitch. Also, I would utilize a higher alpha acid hop at the beginning of the boil such as chinook. Otherwise, it will end up unbalanced, being way more sweet than bitter.
It would be chill haze. The reason the rye beer is probably worse is due to higher protein levels. Palmer suggests a protein rest with high levels of rye in beer. A protein rest should cure your ills.