Hey Uzi,
I don't know your component, but here are some general advises that I can give you. I think that the com_REPLACEnewplugin is outdated and you better follow another plugin - such as the com_docman for example.
It is your decision where you want to show the comment form. If you want you can show it right after the title - all you need to do is to load the comment files on that position.
Something like this for example
require_once(JPATH_SITE . "/administrator/components/com_comment/plugin/com_content/josc_com_content.php");
echo CommentPluginContent::output($row, $params);
so now in your josc_com_content.php you should have a class CommentPluginContent that has an output function
the content of the output function can be as simple as this:
$object = JOSC_utils::ComPluginObject( 'com_content' , $row);
return JOSC_utils::execJoomlaCommentPlugin( $object , $row, $params );
with this code you'll start the component and it will try to see if you have comments for the $row.
Now your $row object should containt an id and catid variables.
You should set the proper id in the __construct function in your actual comment class. (check josc_com_content.class.php)
The getCategoriesIdOption function is only used in the backend for the settings. If you don't need this the way you have it is perfectly fine.
We actually decide if we should render the component in the checkSectionCategory function. If it return false, then we won't execute the component. if this function returns true, then we go further and checkVisual funciton should tell us if we are in single view (for you item view) or on frontpage (library view for you).
If you manage it so far - you will have already the form and you can comment for this item.
The next important function is linkToContent - this function is used to create proper links to the item. It is used in the frontend/backend/rss and emails - so play special attention to it.
Hope that this information helps. If something is unclear don't hesitate to ask. I'll try to explain again
Cheers,
Daniel