As far as the bending of the planks
is concerned: the thinner and wider the planks
are, the more difficult the bending is if you don't want them twisted.
As a "caulking", I usually use the black card (thickness of some 0,3 mm or so) and the result is not a tragedy, I would say (the planks
on the picture are 4 x 2 mm, lime wood.
You have to make a choice of planking
method because everyone has his own "best" one 😉.