I'm externally insulating a concrete block wall with 100mm EPS (50mm between 50x50mm timbers, then 50mm between timbers at right angles). Is it worth taping all the joints between the timber and the EPS? Was wondering if this would help with the performance of the insulation in any way, but was also concerned about trapping any moisture in the timber if I seal it with tape (it has been raining a lot recently...).

Also, do I need to include any sort of membrane before I batten and fix my timber cladding? Is so, what would be best? I have a large roll of Visqueen but would I be better with something breathable?

Chris already has the buildesk software but I would have thought it would be low risk.

I would use a breather paper between the insulation and the cladding. Any air movement will reduce the effectiveness of the insulation.
You could alternatively fill any voids with foam filler.

I put the second layer of EPS at 90 degrees to the first to reduce cold bridging through the timber. The timber is treated by the way. The gaps I've got are too small for foam. Perhaps I should just leave them and the breather paper will help reduce any air movement? Is there any particular breather paper product that I should ask for (I know nothing about them)?