if i delete all the electrum-ravencoin wallet files and folders in my computer (or i try to restore it from another new computer), will i be able to get everything back just by these seed phases? do i need keep the original ledger device(or i could just buy a new one then put the seed phases in?)
You should be able to restore everything if you delete everything from elecrtum-ravencore, or if you install fresh wallet, except maybe labels could be gone from your addresses/transactions, if you didn't create backup for that.