use any login name, but one you will never ever forget. it will also need to be unique, as most common names are already spoken for. if it's not unique, your registration will fail.
after registration, login, edit your profile and change your password to something memorable. doesn't matter at all what yer password is, as long as you can easily remember it.
if you change email addresses, login, edit your profile and change your registration email address - a new password will always be sent, so you'll need to go back and change that new password back to something memorable.