Qn 1:

I have a user_account table consisting of an auto id, email address and
password fields.

The id is made the primary key.  Is that a good idea or should i just
discard the id and use email address instead?

If I were to have the email address as a foreign key in another table,
will the space consumed bigger that if i were to just use the id?

Which criteria should I give more priority to in deciding which way to go?

Qn 2:

CREATE TABLE user_account
(
    id....
    email_address ......
    password .......
    activated...
    ......
)

where the email_addres serves as the username. When a user signed up for
an account, the 'activated' entry defaults to 'off'.  The user will then
have to check his email account and go to a link to activate the account.

What I would like to do is make the email_address changeable and the
user has to verify that the new email addres is valid by again visiting
a link first.

This means that the new email address has to be stored somewhere.

There are two options that i can think of.

1) Create a new table as follows:

CREATE TABLE updated_email_address(
(
    user_account_id...
    new_email_address...
)

2) Store the new email into the user_account table.

CREATE TABLE user_account
(
    id....
    email_address ......
    new_email_address <--------------
    password .......
    activated...
    ......
)

Design wise, which is the prettiest method?
Or is there another solution besides the above two?

Thank you.