Bakecellence
You can make it either with fresh or frozen blueberries, the texture will not be impacted. If you have fresh berries, use them but if you have frozen blueberries like me, no worries, toss them in and you will still enjoy the richness of the berries in the muffin.
Understand that the consistency of the batter will be thick.
DO NOT overmix the batter. Although you may want to because of the thickness of the batter. But over-mixing will develop gluten which will turn the muffins texture harder and tougher, which you do not want.
You can keep the muffins on the counter, in the fridge or freeze them.