For testing, you can get your other account's public key from the infobox.
This is because the calldata size mainly affects the cost of Optimistic Rollup. To test a tx instantly, you can just set the price about 100 times. Then the coordinator will include your transaction because it has aggregated enough fee for proposing.
It currently uses the HTTP protocol to send a transaction to the coordinator. To secure the network privacy, you should use Tor.