Re: Good frequency/key for bassline?
I generally layer my bass. One layer for the actual bass line, and a sub layer of that too. the sun layer isn't always playing an octave lower. Sometimes it's just a low passed version of the main bassline but made mono, whilst the main line is stereo and high passed, normally from around 100Hz-2/300Hz depending on sound, upwards. Then glue together with compression a tad. This gives width and fullness and full depth too to the bass. If the kick isn't coming through so well, side chain it is. That doesn't mean it needs to "pump" that bass either, just duck it enough an short enough to allow the kick to kick through.
It's worth being very surgical with the kick drums decay sustain and release too. It's nice to have a kick full of booming bass, but shorten that mother fucker down if your bassline is playing constantly thoughout the bars it plays in as that'll allow both to breathe a but from each other too.
Some notes will always sound more present with bass due to room setup, monitoring, environment etc etc so it's not fair to say note X will jump through better for you. Because whilst it may do on your system, on mine with a sub it may be the note three below it that really rattles my chest and you can't hear or feel it because your system and setup and environment isn't the same. Hence checking on other systems when you get to a certain stage