First of all, please could you raise questions like this in future as Support Request tickets, rather than Bugs.

The answers to your questions are:

(1) Turning an anchor into a button link is a generic question and you'll find lots of advice and examples elsewhere by searching the web.

(2) See the instructions in INSTALL and systemdefaults.inc.php on how to create custom fields.

(3) You'll need to create a custom CSS file (see the documentation for how) and add a rule

#div_name {  /* where div_name is replaced by the id of the containing div for the field in question */
  display: none;
}

(4) In standard MRBS you can prevent users deleting entries by setting both min_delete_ahead and max_delete_ahead to the same value. However this will also stop them editing entries as an edit involves creating a new entry and deleting the old one. But you probably want to stop them editing entries anyway as allowing them to do so effectively allows them to delete them (for example just edit it to be much shorter and take place five years in the future). If you want to do something more you'll need to modify MRBS code.

(5) As (2)