The simple answer is no. You do not need an estimate before you decide to get your vehicle repaired. The initial estimate that is written is a visual only estimate and does not account for any hidden damage. The damaged area on the vehicle needs to be disassembled to gather the true cost to repair a vehicle. Therefore there is no need to get any visual estimate because it will most likely not be accurate.
Your insurance company may ask for several estimates. There is no law that states how many estimates you must submit or that limits the number the company can ask for. One should be sufficient from the shop of your choice.