I have no idea how much you have to pay for the Roscopanels.
I put the roscopanels about 2 meters away from the window, and in front of the roscopanesl there were 2 frames with diffusion.
I actually wanted to shoot this sequence with a M18 with a 4 meters by 4 meters frame with grid cloth far away from the window but I couldn't do so because of the time I was given to light the sequence.
You could easily achieve the look you're after with the 1.2HMI with diffusion, now, the diffusion you will use will depend on how hard you want the light to be.
I would say that Opal is going to give you a very hard light but you could use a 1 meter by 1 meter frame with Opal in front of the 1.2K and then use something else in the frame, something like Light Grid Cloth for example.
Hampshire is a diffusion I'm using a lot as of lately and I like it a lot!
You can use any small light for the other window, get a net for the window, that will help you a lot.
And if you want fill, you can do so with the joker 400 or 800 with no problem.
I shot that sequence at T2 1/2 (I think); I don't know anything about the Rokinon lenses but if they open at T2 you won't have problems with the amount of light you're going to get.
Make sure that the "rain" is not only water!
Regarding the eyelight I find distracting when there is more than one point in the eye but others don't so you could have a small LED wrapped or dimmed that's right.. or fill from the key side and you will get your eyelight there!
Have a good day.