i can help you with the admin bit but dont have a clue about the 1st problem. Right in your setup.cfg it will say Admin pass. delete the bit called 'password' because thats just the default password. Change the 'password' to what ever you like for example:
// optional: password
//pass=heiko1cruise
thtas just an example of what you do in the cfg. Save it then run the dedicated host. when your joining your game type in where it says 'Host password' or what ever type in 'heiki1cruise'
without the ' '. then when you join yhou should have full admin.
The admin password should be under /admin, /pass is simply a normal password to make a server private. Same concept applies though, just at /admin rather than /pass.
When the user clicks your "Close"-button, you will get a IS_BTC with the "close"-buttons cid in it.
So just look for a IS_BTC with cid=your close buttons cid, When you get this packet, just send a IS_BFN for every button you want to be deleted (you obviously have to know the cid of these buttons).
Just make sure you check the Admin flag in the IS_NCN, and keep track of who is logged in as admin. Then, only execute admin commands from connections that are admins.