I assume your designing planar arrays? If so, I'd
recommend trying out Zeland Software's method-of-moments
EM simulator IE3D. The software will display current
distributions, radiation patterns and give you the
antenna properties. They allow one to get an evaluation
copy of the software which is nice.
as your second question you simply need to reference
the Friis Transmission equation:
You said you already know the Pt, the nessecary
Pr, and the wavelength, therefore once you've designed
your arrays and determined their effective gains
you will know the maximum range of the system.