Undefined Index
The first and third are the same problem:
if($_GET['type'] == "oqeygallery"){}
and
if(is_admin() && ($_GET['page']=='oQeysettings'...
Basically are:
if ( $_GET[‘foo’] == ‘bar’ )
The problme is that $_GET['foo'] is not set. That is, the $_GET array does not have a 'foo' key.
The solution is to wrap $_GET['foo'] in an isset() conditional:
if ( isset( $_GET['foo'] ) && 'bar' == $_GET['foo'] )
Deprecated cap
The second issue doesn’t derive from the code you’ve quoted. Somewhere in the Plugin, a function is using an invalid cap as a parameter. You’ll need to look through the plugin files, to find where the invalid cap – likely an integer instead of a capability – is being used as a parameter.
Edit
Found one: gallcore.php:
add_menu_page('oQey Gallery plugin', 'oQey Gallery', 8, $oqeym, 'oqey_top_page', $icon);
That 8, is a user cap, but is invalid (as of several WordPress versions prior), and needs to be replaced with an actual capability, such as 'manage_options'