Looks pretty good from what you have so far, I usually am more of a PHP Dev when it comes to web stuff but Ill see what I can do, would love to see where it can go (was actually thinking of doing something similar too)
Edit: About the mail send "bug" you have, Im pretty sure it has to do with the way you have it set up for the selector list, Ill see what I can do with it to make it work
Edit 2: Having a hidden value for the coins isnt very smart, your best bet would be to leave that a static 0 server side as a "smart" user could easily fake the post data (I changed that for you)
Edit 3: Found the problem fixed it, script seems to be working fully now, the problem was you had 2 forms which I didnt notice at first, and you were probably thinking they got carried over when submitting again, I wouldve just used a session in php but I dont know how to do that in jsp so I added a hidden form with the currently selected roleid, hope that works for you!
Here you are
index.jsp fix