If the wires are all the same size, the NEC helpfully lists the maximum number of wires by wire type and conduit size. Secure the PVC and male adapters coming into boxes with a metal locknut ...

you can bring your dimensions to any big-box hardware store and have them cut it for you. Then, you'll simply connect the pipes using 4-way connectors, like these Zernmiarder 4-Way PVC Pipe ...

Connectors used include 45 and 90 degree angles, straight pieces, and a PVC conduit box to serve as the mounting bracket. After cutting, dry fitting, and welding everything together the rig really ...