Alpaca issues you a key pair from your own dashboard. Paper and live are separate accounts with separate keys on separate addresses — a paper key is simply refused by the live one. A paper account is free, needs no verification, and is the sensible place to start.
Crypto is spelled with a slash at Alpaca — BTC/USD where your chart says BTCUSD. Tradeus translates both ways, so your alerts keep the name you already use.
Alpaca is not a prop-firm platform, and no firm on the connect screen lists it. If you want an Alpaca account filed under a firm anyway: connected with a key, it goes under the firm you picked first like any other; connected through Alpaca's own sign-in page, the firm cannot travel with it — the connect screen tells you so — and you file it with Edit firm on Broker setup once it is connected. See Connect a prop firm account.