Tune the bass to whatever sounds good and compose a bass line that sounds good with the riff.
You don't have to play an octave lower. You don't have to double. But you can. You also can write counterpoint, pseudo-counterpoint, or other contrasting parts. My favourite is mix-and-match of all of these.
But first thing is to use a tuning that works.
Good luck! The demo sounds good already. But, IMO, having something else that keeps it from sounding too repetitive, like bass, keyboard, and/or good vocals, would complete the package.
You don't have to play an octave lower. You don't have to double. But you can. You also can write counterpoint, pseudo-counterpoint, or other contrasting parts. My favourite is mix-and-match of all of these.
But first thing is to use a tuning that works.
Good luck! The demo sounds good already. But, IMO, having something else that keeps it from sounding too repetitive, like bass, keyboard, and/or good vocals, would complete the package.
