That can Happen coz.. your blog is less with details.. that mean.. You must fill up your blog with some more details about your blog...
Yes you can but take care that the content is not duplicate. Also the sites should not be mirror sites. Mirror sites are not approved by google and you can lose your account.
yes you can add, i added to my 2 sites & 5 blogs but don't use multiple accounts, it will banned you.