As per MacSOUP manual, settings file can be stored in every folder (tipically below your user's Documents), simply:
✓ create an alias for your settings file
✓ name that alias "MacSOUP Default Settings"
✓ move the alias in your user's Library/Preferences
MacSOUP will open it automatically every time it is launched by the user.

In the original message that you want to quote select the text to be quoted, then press the «F» key (follow-up, with or without the ⌘ modifier). Your follow-up message will contain only the quote for the selected text.

Sometimes a subject change can be usefull in order to match better the content of a sub-thread.
In this case the new message subject should be like:

The new subject (Was: the old subject)

MacSOUP automatically recognizes this subject, and further follow-ups will strim out the "(Was: ...)" portion of the subject.

When you see a link you can ⌘-click it, and the link will open in your favourite browser.
Sometimes links are longer than a standard line, then they wrap. MacSOUP can handle also these multi-line links, simply select them before ⌘-clicking.
In any case if you are going to post a link longer than a line it is better to include it in < and >, so that MacSOUP will be able to get the entire link with a ⌘-click also without the selection.