Is this your first board? an 8’ board is definetly achievable, but its going to take you a lot longer to become proficient and shorter SUPs arent as good for cruising any distance or in rougher water. Anyway if 8’ is for you, just make sure you carry the thickness all the way through the tail, if you get your hands on a CI board you will notice how boxy the tail is. If you make the board a little wider this will compensate for the loss of length without having to add to the thickness.
I am thinking of building one for myself. It would be my first project. As I will start a course on wooden boat building, I want to build this board in hollow wood.