Yes, USPS does but UPS and FedEx do not.
No, only USPS can place mail in PO Boxes.
Amazon won't ship to PO boxes due to "Geographic Restrictions". They do allow small packages though, sometimes, it just depends on the scale of your order.
If it fits it ships =)
They usually limit this to 6 years and 7 months.
USPS , UPS Ground, or FedEx Ground
Yes, USPS offers boxes. You can buy them online or in your local post office.
Free USPS boxes need to be processed because the post office has to separate them into delivery routes.
You can get free wholesale shipping boxes on BoxGiver
Approximately 2 weeks to reach your PO box.
It isn't really who won't...because I should think any delivery service would be happy to deliver to one...but PO Boxes, being part of the US Gov't, only allow the USPS to access them and others can't. In fact, the same is true at your house: When Fed Ex or UPS delivers, they can leave it at your door, or anywhere on your property, except they can't place it in you mailbox...not even the notice they tried to deliver something. The mailbox is only for USPS items.
Yes.
You can find out the postal rates on the USPS website. You will need to know the weight and size. You can also get Priority mail boxes which as long as they fit in them they ship.