Do I just need to mail out my Form 1040 after I print it out or are there other things that need to be included as well (invoices, statements, other documents, etc)?

The IRS prefers taxpayer to electronically file the returns.  If the income tax return can't be e-filed because of a certain reason, you only mail form 1040 along with your W2's and other tax forms to the IRS. The invoices, statements, and other back-up documents are not needed, but you may keep it and attached to the copy of your  federal income tax return for future reference.