There is certainly nothing shouting "impossible" from this description. However, we would likely make the circular area behave with most of characteristics of a bullet, including having to be triggered by the shield owner. There are various reasons for that, some being: keeping it consistent with other shields, preventing it from being overpowered (notice you can shoot bullets of other weapons while you have a shield in case of which you would be able to use the shockwave and projectiles at the same time), preventing it from acting out of player's will (when they don't actually want to destroy a given object; although given the theme of the shield you could argue it would be a feature rather than a downside) and the fact that, if you wanted, you could still quite easily force it to constantly produce the force field by using AngelScript while it would probably prove more challenging to make it stop doing so.
Yes, although I suppose a limit of up to 3 per person would be a good idea to give a chance to everybody and potentially stop people from flooding us with half-baked ideas. So yeah, let's go with up to 3 per participant.