Textastic 8 will support ECDSA and Ed25519 SSH keys.

Textastic 8 will allow you to select any installed monospaced font. You can use apps like AnyFont or Apple Configurator 2 to install custom fonts.

This will work again in Textastic 8.

This will work in Textastic 8.

This will be available in Textastic 8.

This will be added in Textastic 8 which will be released as a free update for existing users next week.

Currently not, sorry.