To have watch unchecked by default when making a post, go the 'edit preferences' section in the 'board preferences' tab of the 'user control panel'. This link will take you there:ucp.php?i=prefs&mode=post
You can manage subscriptions and unsubscribe from topics in the 'manage subscriptions' section of the 'overview' tab in the user control panel. This link will take you there:ucp.php?i=main&mode=subscribed
If you want to have a list of topics saved for easy reference on your user control panel, use the bookmark feature rather than the subscription feature. You can find the bookmark link in footer on topic pages. You can also use the 'view your posts' link in the header to see all topics in which you have posted regardless of whether or not they have been bookmarked or subscribed.