I suppose that will work, since it is an idol and looks like a mind flayer. I still favor "sentinel" to "guardian", though. How about "Sentinel Eidolon"?
Sentinel Eidolon's fine by me.
Sure. Any reason to not model it off the psionic power of the same name (and mind flayer ability)?
Only that the original did damage as well. 7d6 to be precise.
That's pretty weak for a monster of its rank, but it isn't them main point of the attack. I'd suggest making it force damage and probably increasing the amount of dice or their size. It also stunned for a set 10 rounds, which is more than the average of 3d4. How about making it 4d4, so the average is 10 rounds?
Psychic Assault (Sp): Once per day, a sentinel eidolon can unleash a potent psionic blast in a cone 60 feet long [or 40 feet like in Dragon 46?]. Anyone caught in this cone takes 7d12 [?] force damage and must succeed on a DC X Will save or be stunned for 4d4 rounds. The save DC is Charisma-based.