Wow, thank you for the kudos!
I'm really glad for you, it's very nice to see you're managing to achieve what you want with s2Member.
About your question on the members login link, which one? The one in WP's meta widget? That should change when the person is logged in. Or do you mean when you add the login link in your post? If the latter, then you'd again use a simple conditional for that, checking whether the person is logged in or not.
s2Member Pro also has a login widget that works perfectly with s2Member and is even usable in the body your page or post with a simple line of code.
Is there a way to call upon the Pro Login Widget directly?
Yes, you can use this PHP tag if you'd like. <?php echo s2member_pro_login_widget(); ?>. For further details, please check your WordPress® Dashboard under: s2Member -> API Scripting -> Pro Login Widget via PHP. There are several options that can be configured dynamically through the PHP tag. It's not required, but you can get pretty creative if you check out the full documentation.