Re: funds immediately leaving electron wallet after receiving from TestNet faucet
Weird, but not that surprising. In past, there are shady ICO/airdrop which give people worthless token in exchange for Bitcoin testnet.
What's weird? Worthless token can be exchanged equally with another worthless token. 
That's good point, but i expect you could run such bot that with pruned node to lower operational cost. ZeroMQ also could be used to notify new transaction on mempool to your own script/application, which eliminate the need of wallet.dat which contain lots of address.
Exactly. You don't need to handle the entire chain, only enforce the consensus rules on mempool transactions, which requires to have verified the entire chain.