Hi Warren,
Aperture for these kinds of photos is not really a concern.
What is important is your desired effect.
These types of photos need consideration about shutter speed and filters.
Night shots usually warrant an open all the way aperture, shutter speed is
important here and tripod.
Try out different filters for your sunsets you'll be amazed and for scenery
shots, well, that depends what you want in and out of focus (depth of
field).
I once took a pic of water smashing against the rocks by the sea in black
and white.  Used a red filter to darker the blue sky and a very slow shutter
speed to blur the water as it hit against the  rocks. The effect was
wonderful (my favourite pic)
My best  advice to you would be to get out there and experiment and have one
hell of a fun time.
Good luck..

Mickey

Start with f8 or f11 and go from there. Whatever gives you a lot of
depth of field.