Do you need to use a jig head with a soft plastic bait?

u can use just hooks and jigs, but the splitshot just helps casting like the jig head and both the jig head and the splitshot work but the give the lure a little different presentation, the splitshot can make the bait swim different

you can use regular hooks but it works better with a jig head. you can tie the weight on the line and the clamp is just to make it more convenient and reusable.

absolutely fine.

Need? No. I've fished soft plastis weightless, I've fished them texas rigged, on jigs, drop shot...It all depends on the bait and where you're fishing it.

Texas rig the baits and use bullet weights. This is the most common way to fish plastics. You can even peg the weight to make the action similar to when it was on a jig head. It will be more weed less also.