I fixed the wiki, it was seriously outdated.. Long story short, you don't need those lines :
$config['calibre_internal_directory'] = '/volume1/calibre/data/';
$config['cops_x_accel_redirect'] = "X-Sendfile";
About your second question, COPS's non compliant search had a critical regression for the last 6 months (At Libitum reported it a few days ago). It's fixed on github but I've not released a new version of COPS for now.
About your third question :
Did you really try fetch.php or is it a typo ?
the correct URL is feed.php. A lot of people are using Marvin with COPS so I guess (and hope) I'll know if it did not work.