cal/mag

It's not too early. Either cal/mag one will help solve your problem. Iron deficiency is typically seen as yellowing in leaves most notably in new shoots, so they probably don't need iron but it probably wouldn't hurt using the plus (which is 2-0-0 btw). It's a bit hard to understand your question but it sounds like you're mainly asking if week 2 is too early to supplement cal/mag. If the plants look deficient, supplement. If you think the plants might be too young/small and can get burned, then I'd recommend just using half the amount and seeing how the plants respond. Usually though, in any case, if the plant looks visually deficient then you should supplement regardless of what week you're on (unless you're flushing the last few weeks or something)