If your going to upgrading your illuminated lightbox diy remember that a second set of lamps will give a second set of heat, so some aluminum ventilation panels fitted to the back to displace some of the heat wouldn’t go a miss and will give a small amount of back-light for you, so your not totally tumbling around in the dark.
On my portable disco lights infinity screens there are two 8 pin bulgin connectors and a flexible cable bulgin lead connector allowing daisy chaining the led disco panel light to the next disco light box. The best bulbs to use are 1w led pygmy and filter gel papers for long life of lamp and low wattage low heat but high price to make your own led disco panel light but in the long run mush better. If you have 40 bulbs a box at 25w and 4 disco light screen that’s 4000 watts if all of them are on at once on but if 1w led pygmy its only 160 watts. The second hand used dj equipment for sale lightfx can be a good way of getting your first dj light screen.