Yes, your Ledger's BIP39 seed is enough as a backup.
-snip- or do i need backup some electrum-ravencoin wallet files in order to make sure i could restore everything?
This is only necessary if you don't want to go through the process of creating a new wallet on a new machine or when you need to format your PC.
If you want to keep a wallet file backup, just copy the wallet file from electrum-raven-equivalent of "
electrum/wallets" directory.