Hi there, for your weight and 20-30+ knots, I would imagine the 115/117 must actually be big enough, also for 5.5 and 6.5 sails and choppy water/your mentioned skill level. No, the 115/117 should be still easy enough to learn some gybing etc skills.
If you were 90-100 kg's, then I would say, yes, rather the 130, but since you mention more wind, then I think 115/117 should be more than fine and I would first try the standard fins, before investing further. We do not put very big fins in the Blasts, as the focus in more on manoeuvres than on light wind/upwind performance.