Feathers do tend to use their full weight allocation. Couldn't say what component allocations people have though.

Your size sounds about right (The Honey Badger is 68cm length x 51cm width x 23cm height for comparison).

The only other thing you may wish to consider is having a different weapon for different events. Extreme Robots and the FW championship will allow the spinner up to a point I think but if you wanted to go to Robots Live, you wouldn't be able to use it.