Copy/Extend Campaign close original?

No, it just creates a new copy of the Campaign, it doesn't affect the original Campaign in any way at all. The original idea behind that feature was that you would play a Campaign for a few sessions, and then when you got to a point where you had a lot of pages (e.g. 20 or 30) that you weren't really using, you might consider "copying" it into a new Campaign, transferring all of your players, macros, and journal entries in the process, to speed up performance. It's not really necessary to do that anymore with the Page Archive feature, since we are much smarter than we were originally about only downloading data you don't have archived. So you can basically use the Copy/Extend feature now to just make a duplicate of a Campaign anytime you want.

Pretty much, yes, Paul. The only thing that would continue to compound is your chat log. Eventually that'll increase in size to a point where it might affect gameplay. You can temporary clear it in while playing your campaign in the settings panel (this gets reset anytime the tab reloads or you return to the game). You can also permanently delete the chat log via the Campaign Details page. If you're the type who likes holding on to your table's chat log, I'd recommend viewing your log from the Details page and saving backups of the resulting html file before you delete the log. Technically I just copy/extend the campaign because I don't feel like trekking around chat log backups. That and this means the logs are all still available for all my players to go back to later and read.