You can just drop your template in the relevant Templates folder, restart DEVONthink, edit the toolbar and drag the new icon to your toolbar. Easy enough.
Your templates should go here: ~/Library/Application Support/DEVONthink Pro 2/Templates.noindex/Toolbar
Works for scripts as well.
About the links: personally I prefer to use the x-devonthink-item links over the automatic wiki links, because it still works independently of possible name-changes of the documents. It requires a little bit more work, but not too much if you use shortcuts like Ctrl-Alt-Cmd-C to copy an item link, for example.