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Only on computer. Needs usb cable connection. Ledger is built to work wirelessly with its own app, ledger live. Not others.
As far as your 2nd question you need to realize you use metamask to transact on the accounts that exist on your ledger. The ledger is not using any accounts you already have on metamask. You give permission for metamask to access those ledger accounts so you can buy, sell, swap and send. So whatever accounts you already have on metamask will have nothing to do with the ledger.
I am assuming you have but I’d take a few minutes and read up a little more on how metamask works with ledger. It’s all on ledger site. That way you know exactly how it works and what you can and cannot. Good luck.