“Surround - iOS client for OGS” would be my choice. For the sub-forum, I think either “Announcements” (same place with OGS-Notify) or “Go Resources” (same place with The Conquest of Go and Katrain) would be good option.
Currently I only plan for Start new games, Analyze Mode/Conditional Move, and Puzzles. What other features need to be implemented before you would consider it “Full OGS functionalily”? Literally replicating all features to the app would take years 