Ok I will complete the rest going across the joists.
With the joists not hitting the edge of the boards am I best cutting them so that the boards all finish on a joists rather than having the ends floating in betwee .
Yes. The taped edges are ok spanning the gap between joists, cut the boards to length so the joins are on joists. If joists are skinny (40mm) consider fixing a bit of batten (25 x 50 tiling battens are ideal) to the joist to make it effectively wider (so you don't have to screw too near the board edge). Ideally stagger the cut end joins
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