safety cable always unless part of a lamp bar which as a bar gets a safety cable but individually is a sort of factory maintined gear for all the fixtures on the bar and does not persay need one each.
As for clamps, what ya clamping to more so determines what type of clamp is best to use.
Normal C-Clamps or others that send a bolt into say an aluminum at best pipe if not some form of thin gauge stand pipe is not going to be as efficient as other types that have either cheseborough or combination of the two sort of friction clamping to the pipe. For steel pipe, no doubt a J-Clamp, G-Clamp, C-Clamp etc of many flavors. For aluminum not so much without truss condom.
All dependant upon what you clamp to, for an I-Beam one thing, for lumber another, for pipe, depends upon what type of pipe.
Always safety cable individual fixtures without a doubt.