Help with PGP Encryption details in java

Hey, we have a ftp process that moves files to external servers and want to use PGP to encrypt the file before they are sent. I read through all the documents and understand how the process works with the public/session keys etc. My questions are regarding implementing it in java on linux specifically:

1) There are tons of pgp packages out there, which one is the most popular/easiest to use?
2) Are there any sample codes that's basically a pgp helloworld and show you how to use pgp to encrpt a file
3) What exactly does the receiver have to do? for example i use a pgp package and encrypt the file and send it to the receiver's server. Now do they have to use the exact same package/version? or will any package able to decrypt the file?
4) From your experience what are some of the things the send and receiver need to agree on first before implementation? for example key bit size? public key? etc.

I am just looking for some good practical advise on starting pgp as have no past experience with any encryption development.

thank you for your time!