How important is it that all cables come from the same manufacturer?

Zero reason why one needs to go all one brand for cables 

I like to mix and match. However,there are some folks that love a certain house sound,and that’s what they like. I don’t think there is a wrong answer. Do what floats your sonic boat. 

not

See, told ya!😁

I have tried many different combinations. In general, different are absolutely fine. I have been fortunate enough to have components that are perfectly neutral, matched and exactly this is what I want to have come out, so as transparent as possible. So Transparent brand are perfect. a full weave of these is perfect and complimentary. However, even with this. I found a Cardas power cord was better for the amp.

Ideally your components are complementary. Because if you add a first interconnect that attenuates the highs a bit, then the second attenuates the bass a bit. Now as you go through you may be balancing the sound but reducing the detail.