I have no experience with pollen gathering, but have been toying with the idea of giving it a try. Part of what sparked my interest was looking at a Sundance II at the ABF conference in January, it appears to be extremely well made so I've been doing a little research on it since then. I think SC hit the pros and cons pretty good...The top is cleaner pollen, as well as easier to put on and take off.
The negative being getting them oriented to the top entrance, also realize that you can't use a queen excluder if you use the top mounted Sundance. I would think the fact that you already have a top entrance would help you some. They seem to suggest that you give them some time to make the transition by partially closing the bottom entrance for a few days, then completely closing it off. After using just the top entrance for several days or so, then place the top mounted Sundance trap on.
The other suggestion I've seen that seems to conflict with a lot of opinions is the practice of not removing on bypassing the trap every few days. They claim the "on again, off again" approach stresses the bees more...Whereas if you leave it on, the bees will adjust their foraging to bring in enough pollen in spite of what the trap is collecting.
As for the processing, some refrigerate it and then dry it, while others simple freeze it and sell it that way. Some think drying it makes the flavor "less pleasant", so I think freezing it sounds like the better/easier option...Unless there's a problem with that method that I haven't seen. Lastly, the consensus seems to be that daily collection is very important to avoid mold, pest and other problems. If I remember correctly, they say a Sundance on a strong hive can bring in 1 1/2 to 2 pounds of pollen a day....That's pretty darn impressive!