tldr: A little bit more than 400 million billion billion standard 2x4 bricks, roughly.
Given my calculated radius of 9.39E6 m (47% larger than earth), the volume of Lego Planet is 1.95313E21 m^3.
Brickepdia[0] (of course that's a thing) shows that a standard 1x1 block of standard height is 8 mm x 8 mm x 9.6 mm, or 6.14E-7 m^3. A 2x4 brick would be 8 times that, or 4.92E-06. Simple division then gives us that Lego Planet is made of 3.97E26 standard 2x4 bricks.
