Does WordPress perform better with curl installed?

WordPress will use curl if available and it is first transport choice, that is preferable to other supported methods of performing HTTP requests. There is plenty written on merits of using curl and that’s not really specific to WordPress. From the top of my head I’ve read Requiring cURL in Your PHP Library recently.

couldn’t connect to host – wp-cron.php?doing_wp_cron

You should open a support ticket with your host, as it’s probably related to their environment. From the error, it sounds to me like they might be blocking curl in their environment, probably for security reasons. They may be able to unblock it, or you may need to find an alternative.

throttle/limit a logged in user’s http requests to specific page on a per day basis

First, check for get_current_user_id. Then create a log of visits by adding information to a user’s metadata with update_user_meta & get_user_meta. On every page hit that you care about you can run a function to determine rate/limit of usage per user. If they break the rules, you can redirect to a page that doesn’t contain … Read more

Hata!: SQLSTATE[HY000] [1045] Access denied for user 'divattrend_liink'@'localhost' (using password: YES)