I need some input here.

What would be the minimum necessary internal surface area for an Island 3 style space habitat to maintain a a background count of 0 in the interior and a maximum BC of 4 between the two cylinders, assuming that the entire usable surface of the habiat is dedicated to rain forest?

Somewhere in the neighborhood of "That's no moon."

You're not going to get up to a BC of 0 in a space station. I think the canon stations have a BC of around 4 at best.

Any recent info on SR space development? It is my understanding that SR space stations tend to be rather small, with perhaps a few dozen crew members.

Bog standard O'Neill cylinders have 392 square miles of usable surface area, five miles of sky, and are designed to support a population of 5 million humans in relative comfort. They look something like this. An Island 3 colony has two such cylinders connected with a long rod along with two agricultural rings.

Those are "That's no moon" in size.

The ISS is only about the size of a football field and I can see it from my backyard.
Wake of the Comet is the last thing that really delved into Shadowrun in Space.

Was Wake pre or post Target: Wastelands?