The Lesser version sounds like a limited, but wider version of Dream, or Sending

How to determine if the message has been conveyed :
  1. via a spot (or listen) check to determine if the target realizes it is a message (DC=40-perform check)
  2. then roll a straight intelligence check (DC=25-CL) to determine if the target understood the meaning.


I give indicatory DCs, they should be adjusted through playtesting ...

Enchantment is the appropriate school, Compulsion the appropriate subschool, you should add the mind-affecting and dream descriptors, ie :

Enchantment(Compulsion) (mind-affecting, dream)
not sure if the dream descriptor exists, but you should add it anyway, so you can mention it later in your feat, ie :

"This feat allows you to add all spells with the dream descriptor to your known spell list"
Long casting time, short AoE, high potential number of targets, mostly irrelevant duration, this would make for a 5th or 6th level spell (you can touch more targets than the Dream spell, but the message may not be conveyed, which vies for an almost equivalent level, adjust according to the DCs)

Greater version should be 8th at least (very long range, extreme duration, potentially thousands of targets, and i'm sure you'll reduce the understandability DCs)

Make them one level lower for Clerics or Bards, as dreams are one of the gods's favored means of communication, and Bards's stories are frequently the cause of people's dreams.

ie :

Lesser ...
Level: Cleric 5, Bard 5, Sor/Wiz 6

Greater ...
Level: Cleric 7, Bard 7, Sor/Wiz 8

Hope this helps

Cya