Hello,
To deploy solutions like that will require quite some coding.
To answer your first question - there are multiple ways to solve it.
Fastest way to do that is to modify the tpl that displays tasks. You can find it in /data/Base_Theme/templates/default/CRM/Tasks/default.tpl.
In that file you can reorganize the way fields are displayed. Make sure that your custom fields aren't added automatically, by extending the if condition you can find in line 146.
If you make any changes to this file, make sure to create backup of this file outside of /templates/ folder, since it'll be overwritten after the update.
As for the 2nd matter: from what I understand all you want is to set default value for a field, for all new records created.
If so, and assuming we're still talking about Tasks, fastest way to do that is to modify modules/CRM/Tasks/Tasks_0.php, find line 24:
$this->rb->set_defaults(array('employees'=>array($me['id']),'status'=>0, 'permission'=>0, 'priority'=>1));
And add necessary values there.
Both solutions are not permanent solutions and when upgrading epesi you will need to re-apply these solutions. If you want more permanent solution, I can help with that.
Hope this helps.
Kind regards,
Arek