"molding" on ceiling

[MarkAndDebbie]

I really like the Hal Nash's cabin. We think we'll do beadboard on the ceiling like him. However, he said it was a pain to cut all the insets. I was thinking of just using the whole sheet running the 8 foot horizontally. This would give me seems every eight feet. I thought I might get a thick rafter look by trimming the seam with a 2x4 or 2x6.

1. I thought I should rip off the rounded edge of the 2x (is there a name for that?).  I wondered if I should also route a groove for the 2x or if you wouldn't notice it was fake from the ground.

2. 2x4 or 2x6?

3. only on the 8 feet seams or would it not look right and I should add them every 4 feet?

4. do I need to be concerned about the extra weight since these aren't providing any support?

5. just nail them - or more?

Thanks,
Mark