One time change field + personal comments I'm not very familiar with all the modules for Drupal. Therefore, let me try to explain what I'm looking for.

1) The users shall be able to create nodes with some specific fields. Some of those fields shall be writable only one-time.

2) To this node only the author and users allowed by the author shall have access.

3) Additionally the users who have access to nodes of another user shall be able to make comments (including attachments). Something like a discussion forum to each node, but only the author of the node and the creator of the comment shall see their nodes.

Hope it's somehow understandable.

Are there any kind of modules for any of the above requests?
If I understand the problem. You can write hook_form_alter() in custom module and disable needed fields when user edit node. And configure permissions on this page admin/people/permissions