I don't think there is good reason to split according to M-B groups. If you want to split according to personality, the Big 5 factors are the current consensus. Even then though, I don't know how advice would be specialized to low agreeableness individuals, for instance.

The broad categories come to my mind are

• Epistemic
• Instrumental/anti-akrasia/motivational
• Social
• Creativity/seeing with fresh eyes
• Quotations

You could either bundle these with the instructions to pick a single one to focus on or if you have room for customization, let people pick whether they want a high or low amount of each in their stream.