@sbrajesh the following function suits purpose #2 just fine. I think the var $user_url which seems tied to the main site url is safe enough (untested for sure). fingers crossed.
function bn_loggedin_user_domain() {
global $bp;
return $bp->loggedin_user->userdata->user_url;
}
add_filter(‘bp_loggedin_user_domain’,’bn_loggedin_user_domain’);
