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.

You can drag the file icon from the window title bar in Textastic onto the Safari Dock icon to view it in Safari. This also works great with Markdown files when you drag the file icon onto Marked 2's Dock icon.