So are they butt jointed boards? Do you need to paint the plywood backing before boards are installed?
What type of wood is used for 1 x 8's?
So is installing over plywood cheaper than over drywall? Any advantage for either?
Your work is great and I really appreciate your help!

The boards have a rabbetted edge, so no plywood shows. The wood in this case is poplar, but maple finishes even better. The plywood is structurally better, but sheetrock is less expensive.

what size planks on the ceiling? in terms of plywood over sheetrock, how was the plywood sealed to prevent air infiltration....in the case of sheetrock tape and mud helpts reduce air infiltration. i thinking about doing shiplap in the living room and wondering if using 1/4" with 1/4" sheetrock over would be good? maybe this is overkill or not neccessary.

1x6 v-groove boards on the ceiling. The exterior walls of this house have closed cell spray foam insulation (no air infiltration). Min. 1/2" plywood for backing.

I love the entry door ! Can you tell me where I might order it ?

Front door - Millwork Artisans, Charleston S.C. millworkartisans.com

What color paint on horizontal boards? trim the same I assume? Thanks!