There is no real answer to this question, just a rough estimate:
Unfortunately, the fluency needed strongly depends on the materials absorption behavior and the laser used (pulse duration, wavelength) which makes it impossible to give a value as an answer.
I would however suggest searching for the ablation treshold of your materials system - this might already have been published somewhere. This will set the minimal value for your fluence.
However, depending on the geometry of your setup, especially the distance between your target and the substrate you are about to coat, you might need much more fluence to gain a reasonable deposition rate. Think of a multiple of the literature treshold value.
You will have to conduct experiments to find the real values.
Really, for corrected answer needed know more details: (materials, size of the target, wave length of laser, repetition rate, pulse duration, spot diameter on the target). Also, what type of the deposition sheme do you use (direct or back deposition). After that we will can give you the answer.
You should figure out the ablation threshold as suggested rightly by Bjorn.
Second achieve a resonable deposition rate.
Secondly you film should be smooth enough, so that you can avoid putting too much energy into each short, and obtain a rough surface, with particulate matter on the film surface.
The desired stoichiometric transfer should occur, and you shouldbe able to measure the final properties, in your film, and thereby you can decide to work at that energy.