I hear you, @joergkutter. Maybe it would make things a bit easier if you could determine a common or complementary thread/theme in the courses you have?
For example, a lot of technique-oriented courses share common material, but have different approaches or structure.
The same is true for courses in theory, ear training, arpeggios, scales, genres, etc.
I realize everyone is different, but I find it fun and, for me, useful to approach learning bass by viewing it through different lenses at the same time. But, again, everyone is different and to each his/her own.
Above all, though, you own some sweet basses, so life is good. 