Qbittorrent version 5.0+ has the settings in the web-ui so if you are setting it there you can ignore that part of your tutorial where it says to use qbittorrrent.conf (its the same).

You are correct about automatically appending trackers.

To verify its working you should be able to add a new torrent, look at its trackers and see the new .i2p trackers added. They can be a little slow to connect initially.

Yup totally possible. You need i2p running with a SAM bridge. Last time I checked there are two releases of qbittorrent, one supports mixed mode for i2p. I believe it is the one that says lt20. Check the box in settings for i2p and mixed mode, set the IP and port for your I2P SAM bridge, auto add i2p trackers and you’ll be cross seeding.

Maybe Picoshare

I have a couple, just acquired recently. Pretty neat!