Hi, as to your first question im not sure on that one.  I suppose you could block out the sign in other than the facebook and add this code for the switch

    $isModerator = OW::getUser()->isAuthorized('base');
     $isAdmin = OW::getUser()->isAdmin();

     if($isModerator || $isAdmin)
     {
      //show your normal log here 
      }else{

                //show the facebook only login

              }

as to your second question, there are a number of things on my other site you can try.

stopspambots.org/tipsandtactics.html

that page has some good tips..   Also get the question captcha, its free,

http://www.oxwall.org/store/item/583

i use that and its great.  You have to know how to write the questions so the bots cant google them, yes bots can google answers sadly :(    if you need some tips on how to write the question i can help.

hope that helps :)

Quote from Taissa Eman, have you solved your issue with the help of the dave's tips?

And please, be note, one request per one topic. Create a separate topic regarding issues that are not related to the Facebook sign-in.

You can hide the sign-in label via css

.ow_signin_label {

    display: none;

}

and you can hide the sign-in button on sign-in page: 

.ow.base_sign_in form .ow_sign_in span.ow_button .ow_positive input{

display: none

}