LOL
When a seed first sprouts, you have NO clue to its genetics or what/how it will do.
The first leave (when the seed shell cracks) don't count for crap.
The second set start to support the plant. (first node)
Its kinda useless to worry about a plant until the 3 or 4th node. (IMOHO)
I'd be aware of the distance between the 2-3 and 3-4 node and looking for stretching. And when those first nodes start their own growth/nodes.
Let the seedlings grow before worrying about them.
I'd hold off on the fan until next set of leaves are *there* (not just peeking out) Although a fan is a bit subjective. CFM and distance and air speed are vast, so your mileag will vary (right now. I just grab my plant and shake it every time I check on it. But its belly height)