Is there a way to get the category and album listings show WHERE users are browsing, and how many users are in the current gallery?
I'm not aware of such a mod. The place users currently are is not being recorded, so a mod that could possibly accomplish what you're up to wuld have to store the page the user is currently looking at int the database. Would cause a lot of additional queries. Therefor, if you plan to code such a mod (or hire someone to code it for you), you'll have to understand that it will be resources-intensive.