Suspended platform hanger support spacing calculation
You want to support the equivalent of 18.75 lbs per square foot which is a relatively a lot of load compared to what your ceiling is designed to support. You will need to reinforce your ceiling or provide an alternate support structure.

You need a minimum of (4) supports for it to be stable. Supports at each rafter or joist will spread the load better.

There is no hardware that couples threaded rod with a lag screw.