For the blending problem, you should be able to replace the opengl calls with blendMode(ADD). This is a new function added in Processing which sets screen blending with OpenGL under P2D and P3D for most of the blending modes supported by blend.
Enclosing the drawing calls for your semi-transparent geometry between hint(DISABLE_DEPTH_MASK) / hint(ENABLE_DEPTH_MASK) could help to minimize artifacts due to the lack of depth-sorting.
About the noise that appears momentarily when the sketch starts, this is an acknowledged issue.