Yes, for my taste the patterns are a little too similar in type and scale, although tattersalls are classic with a tweed. The effect is made a bit worse by the similarity in colouring and the fact that you have no patterns anywhere else. I think that with any brownish tweed it's difficult to go wrong with a solid light blue shirt.
I think tweed jackets go well with denim generally (much as I would love to advise you to bust out the full rig with moleskins/cords, sweater vest, tie with little pheasants on etc.) - but perhaps here the jacket is a bit too fitted against the bagginess of the jeans.
Kai, I really like that herringbone and you look very warm indeed.
I can only agree. a solid blue or a blue with vertical stripe (soft red maybe? can't see the colours properly - pick a colour that is a minor colour from your jacket as the stripe) shirt would be better.
A nice V neck thin jumper in a solid colour too would look good if you want to make it a bit more formal. I think you have the right idea with the jeans, try smart and worn to see what a difference it makes.
I love Kai's stuff - I want that overcoat - beautiful.