If I play a token unit can I apply Legion if I didn't play anything else?

No, you cannot apply the Legion effect if you have not played any other card that turn.

According to Rule 812.1.c, for a Legion ability to become active, a card different from the one with the Legion ability must have been finalized on the same turn. Since Legion requires another card to be played first to satisfy the condition, playing a token unit as your first action of the turn does not satisfy the requirement for itself.

While playing a token unit does count as "playing a unit" (as confirmed by RiftJudge FAQ #9440 and FAQ #9833), Legion specifically looks for another card to have been played earlier that turn. Because you haven't played anything else yet, the Legion dependent ability remains inactive.