1) Why multiple transactions? you can give higher fees for a single transaction which will still give it higher priority 2) Unless you are a malicious BTC\ETH

1) Why multiple transactions? you can give higher fees for a single transaction which will still give it higher priority 2) Unless you are a malicious BTC\ETH mining node that got the future transaction (which uses the nonce again), it will be too late. You will learn about the re-use only after the blockchain update propagates.