Hey! i was wondering can i solder some of the leds in place and they will light up, or do they alla have to be in place?

Might be worth to mention that there is gona be an empty X in the middle (until i get the right leds..) so some rows are gonna be empty room in them, can i still safely turn it on or do i have to wait?

You can go ahead and turn it on with any number of LEDs, right down to one or zero. You will probably *not* get good LED brightness uniformity while there's a set of missing LEDs, so don't be surprised by that. If you plan to run long-term with a partial set of LEDs, you should program *just those* LEDs to be on, so that you do get good brightness uniformity.

like he say above i m agree with him that the best solucion is to switch the brightness between 0 and 1