To get a feeling of the actual size of the grid at different spacings I decided to print a few samples on paper (and taped together to full size). I tried 30mm, 25mm and 20mm spacing.
My original though was that 30mm maybe was a bit on the small side, bu after printing it I discovered that it rather was too big.
I settled for 25 mm (about one inch) between the 5mm LEDs.
Around the grid of LEDs there will be a frame made out of two steel wires for the power distribution.
Then the oscillators will then be freeformed and put between the grid and the frame.