Roots- Here's my take on it. Rockwool is NOT a beginner medium by any stretch. I assume that by the time you are running RW slab you know the plant well enough to judge when to tear off the individual cells from a breakaway propagation slab like that. Plus, if you turn the prop slab over, the cells are deeply cut from the underside, making them easier to tear off without damaging roots.
Fan- You need a fan but it is a balance between air movement and air drying. A light breeze, almost too faint to notice, just enough to barely move the plants, is sufficient for seedlings.
And no matter what your medium, seedlings require extra care and attention anyway to keep the moisture level appropriate.