If we DO have more then one character, are we allowed to use more then one in a single RP? And we're aloowed to have as many as we want, as long as we keep them active yes?

Yes to both, though I do caution you against having too many of your own character in an rp, too often. It's really off-putting when a person sits there and talks to themselves, and really, it's boring for everyone, unless you like talking to yourself at length. ^^