From what I understand, using another layer of encryption (ssh) over the tor network is redundant since it is already secure.
You think tor is the same as I2P? Well, from my personal experience I2P is much better at transferring big files. 99% of the I2P traffic must be torrents using the i2psnark implementation of torrents on the I2P network.
I don't know how strong tor's encryption is compared to what you get with ssh, but I'm quite sure that if you use I2P there is no need for extra encryption. You might as well use ftp instead of sftp.
There is also no need for special authentication of the server. That is also guaranteed by the tor or i2p addresses which are cryptographic signatures.
On tor, addresses look like kpvz7ki2v5agwt35.onion
On i2p, addresses look like
lnQ6yoBTxQuQU8EQ1FlF395ITIQF-HGJxUeFvzETLFnoczNjQvKDbtSB7aHhn853zjVXrJBgwlB9sO57KakBDaJ50lUZgVPhjlI19TgJ-CxyHhHSCeKx5JzURdEW-ucdONMynr-b2zwhsx8VQCJwCEkARvt21YkOyQDaB9IdV8aTAmP~PUJQxRwceaTMn96FcVenwdXqleE16fI8CVFOV18jbJKrhTOYpTtcZKV4l1wNYBDwKgwPx5c0kcrRzFyw5~bjuAKO~GJ5dR7BQsL7AwBoQUS4k1lwoYrG1kOIBeDD3XF8BWb6K3GOOoyjc1umYKpur3G~FxBuqtHAsDRICkEbKUqJ9mPYQlTSujhNxiRIW-oLwMtvayCFci99oX8MvazPS7~97x0Gsm-onEK1Td9nBdmq30OqDxpRtXBimbzkLbR1IKObbg9HvrKs3L-kSyGwTUmHG9rSQSoZEvFMA-S0EXO~o4g21q1oikmxPMhkeVwQ2VHB0-LZJfmLr4SAAAA
I2P's encryption is probably much better.