Your i2pmail address isn't directly linkable to your torrents unless you happen to post torrents to trackers with your i2pmail e-mail address embedded in the tracker information. If your i2pmail address uses the same name as your postman account, then people may be able to guess your e-mail address from your postman account name.

Generally, as long as you keep your I2P identity separate from your clearnet identities, you should be fine. If you don't want to be identifiable as the same person on various services, use a separate identity for each service that requires a login.

Regarding seeding torrents, if you're the only person seeding a torrent, then a restart of your router will give you a new I2PSnark destination but may still reveal to the observant that your old destination and new destination correlate. On the other hand, if you're one of many seeds, it's difficult to correlate your previous I2PSnark destination with your new destination.

For extra peace of mind, you can configure I2PSnark to delay starting torrents for a longer period post-startup to make correlation even more difficult.