BuddyPress.org

What I am going to do for a while, is I as admin, will approve or disapprove membership to the site.
That along with cache plugins.

@psivait

re spam: I would do a little research as there have been some lengthy posts on this question /issue here so dig those up and give them a good read, there are plenty of steps you can implement to reduce spam, however be aware that there isn’t much you can do about human spammers and they account for a good deal of time wasting these days especially if you allow for blogs to be created at signup (something I don’t personally think a good idea).

As for approving multisite blogs as a single super_admin I’m not sure you can or should, multisite blogs are meant to be fully fledged blogs in their own right and the user that creates the blog is the admin. There are however steps you can take as the multisite admin to restrict what can be done on user blogs but that is more a question for WP than BP. If your meaning that you will have members on your primary blog that is running the multisite install and you want to elevate them above ‘Subscriber’ level to say ‘Contributor’ so they can post then that can be done and can and submissions will be ‘awaiting admin approval’ which you will see if you run through the options in the dashboard with perhaps a test user with a ‘Capability’ higher than ‘Subscriber’