Glad to see the art being used by more than just me. It fits the theme of "Heir" quite well.
(1) As for the card, I'd recommend the following:
If you're striving for simplicity, this card seems to be doing two completely different things (top-decking and Coffers gaining) that have little or no impact on each other, so I'd turn this into two different cards. The top-decking an in play card effect is incredibly strong and interesting enough that I think this is all one card needs. The Coffers gaining is interesting, but a few, potential pitfalls should be addressed:
(A) In no way do I think this can work if the maximum amount of Coffers you gained is tied into the number of players there are. Cards should be relatively stable and play the same no matter how many players. Pirate Ship is an exception, but even then increasing the number of players only increased your chances of hitting a Treasure; it does not gain you more Coin tokens. Imagine if it did though. I could get my Pirate Ship up to +$5 Coin (5 Treasures revealed) on the very first play, and probably +$10 (another 5 Treasures revealed) on the second play. Now I just play Pirate Ship for +$10 and empty the Provinces (or Colonies) in no time. It's so powerful it just makes the game not fun. So I highly recommend making this a fixed amount of Coffers. On a duration, cantrip, +1 Coffers or +2 Coffers is plenty.
(B) I would try and make the condition on the cards that are being counted for +Coffers as broad as possible. Counting just Heirs would have been problematic because if one player wins the split, they have a huge advantage over the other player. In a 2-player game that would be unlikely given they both have a fair shot at 5 Heirs, but in a 3-player game it gets really tricky. If everyone rushes Heirs, one player may end up with 3 Heirs to everyone everyone elses 4 Heirs simply because of shuffle luck or player order. Of course it's a bit better to include other Duration cards, but I still think this is too small of a pool of cards. Durations are uncommon enough that it might just end up being the Heir pile that is counted. So something broader like: (1) Cards with 2 or more types, (2) a certain cost range, or (3) comparing cards you've played this turn to cards others have in play all might be a better fit.
Even with these changes, a cheap, cantrip, with little side effects might lead to games where everyone rushes them, or no one touches them. Only playtesting can answer that though.
Hopefully this has all come across as more supportive then critical. It's an interesting idea, but cards like these can be very tricky to get right. I wish you luck and if you need any clarification on what I've said, I'll try and explain more clearly at another time when I'm not rushed.