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-Ravencoin-equivalent of "
electrum/wallets" directory.
Or use: "
File->Create a backup"
do i need keep the original ledger device(or i could just buy a new one then put the seed phases in?)
It's compatible with any hardware wallet that supports BIP39 seed; same model, different model or from other brands. (
check its backup phrase compatibility)
Even software wallets support it as long as it supports BIP39, but that's only an option if you do not have any choice.