To make a digital billboard work (and justify its extremely high cost) you have to have the right mix of 1) visibility 2) traffic count 3) quality of traffic. On the visibility side, the sign needs to have no obstructions, a "head-on" low-to-the-road exposure and typically be a right-hand read. The traffic count would need to be, in my opinion, at least 50,000 to 100,000 viewers per day. The traffic also needs to be desirable "quality" -- typically an upscale area with a shortage of competing ad messages.
Digital signs do typically require additional permits in many markets. Consult the city or county. You will also need greater power requirements and special engineering to support the weight.