Should I choose different brushes for calligraphy versus sumi-e painting?

Generally yes, though many brushes can do both.

Calligraphy brushes (shodō fude) tend to have stiffer hair and a more tapered tip, built for the decisive, controlled strokes of characters. Sumi-e painting brushes are often softer and hold more water and ink, allowing for the delicate gradations and broad washes typical of landscape and nature painting.

If you only want to own one brush to start, a medium-stiffness mixed-hair brush is the most versatile choice between the two.

🔗Kenmo Shou ( small ) Kana Joufuku brush

🔗Kenmo Dai ( large )  Kana Jjoufuku brush