Dunno. You can look at their pricing tiers for yourself: https://asana.com/pricing. Also, it's not obvious that the Premium tier and above, despite saying it's "per person/per month", it's 5 person minimum. Gah
No there isn't a limit, like the person you are replying to, I am on a 2 seat plan as well. Total costs: +/- 26 euros a month.