no you cannot unless you make a different email but no you cannot do that.
On most email systems you can (such as mozilla, hotmail etc...).
Should be able to. Most e-mail programs have a limit of 10 MB. If you try to e-mail more than that, your message will not go.
It isn't necessary and is often confusing to have more than one email account. It may be useful in separating work from personal communications.