Should I reset the blockchain transactions in Multibit Classic before I sweep my private keys into my electrum wallet?
Nope, thats not necessary. The resetting of blockchain doesn't affect the network as a whole, it just makes the client reload all the transactions.
Or is simply sweeping my keys sufficient to get the btc from my earlier failed transaction? thanks
Check if the transaction on Blockexplorer.com. If it doesn't exist, you're fine.