Question   On the join page how do I remove the redirect url?

A. The name of the you is:
http://YOURDOMAIN.COM/join

Your can edit the template file for it at:
http://YOURDOMAIN.COM/adminpages/join.html

A. With PayPal, after a person pays, they are required to click a button (that is not noticable to many people) to continue back to your site to finish the join process.  This can cause many people to get stuck in the PROCESSING mode.  With PayPal, you can have it to automatically redirect to your website after payment so the person is not required to click on a button to proceed.  To do this, you must turn this on within your PayPal account.

A. When logged into the admin go to "Advanced Features" then click on "Misc".

Remove any value in the "Redirect Page" field so it is blank, then SAVE your changes.

A. Yes, it's editable by editing the .html file in the File Manager. 

The file you would edit is:
/adminpages/welcome.html

A. No, it is not possible with Direct Pay to have someone first make payment before creating their account.  They MUST create their account before payment for things to track correctly.