You could hire or buy from £50 a SDS drill. Most of them have a 'rotor stop' function so they can operate on hammer only and can be used with a chisel bit to remove mortar.

You can buy Brick Cleaner from a builders merchants. It's mostly acid which dissolves lime stains. It all depends how clean you want the bricks to be, some folks like the look of old, reclaimed bricks.

Good luck with the project