Is it preferable to buy bindings of the same brand as the board? Does it matter?
It doesn't matter, and it's often not even possible. Some board companies, including some beloved on this forum (e.g., Never Summer) don't make bindings. Some binding companies (e.g, Union) don't make boards. These companies would have few customers if matching actually conferred a tangible benefit.
Sometimes it can be to your advantage, in terms of ensuring a good fit, to match bindings and boots
from the same manufacturer. But that certainly isn't necessary either, since you can simply try out combinations until you find a good one.