2
I can answer the first question, but not sure about the second.
Basically all changes are made in the contactform.php file under the contact module. Is, say, u want to remove the location files, then delete lines: 33 and 42 which are:
$location_text = new XoopsFormText(_CT_LOCATION, "usersCompanyLocation", 50, 100, $location_v);
and
$contact_form->addElement($location_text);
The best way to learn these things is to install a local copy of XOOPS on your machine and play with these files. To install a local copy, look for something called XAMPP on the forums.
Now, to add a field, just duplicate one of the existing fields in the same files making sure you change the variable names.
I hope this helps.
Cheers,
Abdala