Originally Posted by mic3756
The bass isn't your chord progression, it's a part of your progression (the lowest note) so if you chord is A minor you'll have your A in the bass. You could use an inversion and put a C or E in the bass, but you can't really put anything else otherwise it won't be an A minor anymore. There's only 3 notes in a chord so if you use 5 instruments you'll have to repeat one of the notes twice (which is fine). You can also use other notes that are chord additions, and inverse the order of the notes, and place them in any octave you want.
As for which scale, there's no way to know, the notes are c# d# a#, there's many scales that use these notes, you can use any of these scales and it will sound good. Since it ends and begin with C#, and that C# minor doesn't use A#, a good option would be to do it in C# Major.
When you choose a scale just google it and look on wikipedia what are the triads of that scale.