moving from imap to pop3; splitting w/links; tagging

[subopt]

I've started using Gnus with my IMAP account, trying to sort out all
the concepts and config vars. Our IMAP server is so slow and buggy,
however, that i'd like to start fetching from our pop3 server, and
download all messages to my home dir.

I'm still pretty unsure of what i'm doing though. Can someone show me
what i need in my .gnus file to do the following? :

1. Download all messages from my pop account to ~/gnus-pop-email/.

2. Delete all downloaded email from the pop3 server.

3. Don't delete any local copies of any message until i specifically
   mark it to be deleted.

4. Always show every message i've fetched until i either delete it or
   score it below the standard threshold.

5. Set up splitting so i leave the actual messages in the INBOX, and
   just put links to them in their separate filtered boxes.

Also, what i'd really like is tagging. Is this currently possible?