5. AFAIK :
- Disable pruning/prune mode
- Enable txindex
- Enable server and configure rpcuser and rpcpassword
It might be different since i tried LN on test-net, not main-net almost a year ago.
6. You either can modify bitcoin.conf or add -port=n to startup parameter, but i'd recommend modify bitcoin.conf for your convenience.
Updated bitcoin.conf example : https://github.com/bitcoin/bitcoin/blob/master/share/examples/bitcoin.conf