Hi Legion -
I would use usps click and ship - create an account there, and then click "ship a package with postage"
The web site will walk you through the process - filling out all required custom forms along the way, and then when you print the label it is all consolidated on the label, your postage is paid and all you have to do is drop the package off at the post office.
Your first pass through the website can be a pain, but once you understand what is going to happen, it is great!
best regards -
mqqn