managed links in Wysiwyg?
I would recommend that you base your solution on the ckeditor_link module. To use this module, you will of course need to be using ckeditor for your wysiwyg editing.  If this is not a problem, then users will be able to use a new "Internal Link" URL type when creating links.  Typing in the node title of the target will make a link to node/1234, and this link will be transformed into a link to the node's path alias at render time.  Now, your internal links will automatically change if you edit the path alias of the node; there is nothing else you need to do to manage them.

For external links, I would make a new node type for external links, and make a landing page for each one.  Use a link field on the landing page to hold the external link, and put boilderplate text in your template for that content type.  Once you've set this up, you can again use the ckeditor_link module to target your landing page.  If you don't like the idea of a landing page and you're a little handy with coding, you could make your own version of ckeditor_link for external links, and modify its input filter to render the URL of the target link instead of the URL of the landing page.