You can add Announcements and Openings compulsory in Forum ??
If by an announcement you mean a forum thread that is displayed on each forum board, then uCoz does not have such feature. It is possible to create announcements (sticky threads) within a certain board only.
If you purchase a Basic Account, Can I add advertisements and openings compulsory?
What do you mean by "openings"? You can add advertisements to your website even if you are a free user. If you mean uCoz advertisements, the uCoz banner will not be displayed on your website if you buy the Basic package.
I'm not active on the forum anymore. Please contact other forum staff.