Just put a few diagonals between a few uprights - top to bottom going one way to the center and same going the other way.
When I built my garage years ago it was on the same principle as yours I put felt all around it floor to roof before the ship lap and also like you overlapped
it over the base. It's still there today looking just as good as when I did it 30 odd yrs ago.
The double door frame was made of 3x2 angle iron concreted into the ground and there was another half way down just to stabilise the framework along with all the other cross bracing.
Sorry about pictures - they are copies of photos and I have miss laid most of them