If you did not verify the Electrum binary's authenticity, then you probably have a fake copy and that is probably why you are losing coins instantly. I always check that all the GPG signatures match before using a new version of Electrum.
Which is pretty weird, because thieves aren't known for stealing testnet bitcoins.
Weird, but not that surprising. In past, there are shady ICO/airdrop which give people worthless token in exchange for Bitcoin testnet.
.. Then, you have a full node that must run 24/7.
A good bot should have some good infrastructure.
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.