OK so i decided on a spider dolly (they are closed or I would have had one for two weeks already) And now the question is should I get a fourth arm even if I am only using the three arm setup with tripod, no platform or seat? I mean, will the fourth arm help it to track more smoothly and be more steady than just three?

Also should I get channels and spreaders?

And finally are there any alternatives I should consider?

Stephen Eastwood
http://StephenEastwood.com