wordpress metaWeblog.newPost xmlrpc create category if not exist, and prevent duplicate titles from codeigniter
Re- 1st / 2nd.
You can use wp.getTerms to check if category exists.
Add the category using wp.newTerm
Create a post using wp.newPost
Re- 3rd.
Can I post multiple posts in one xmlrpc request ?
No, not to push in content.
Nonetheless if you do have access to the WP installation you can create a small plugin that would pull content from a feed and insert_posts after a remote trigger from your CI application.