If you're planning to customize clothes, use Spine's Skins feature. It will help you a lot with visualizing and animating different clothes.
Also look up "mix and match" in the forums. This isn't an official feature of Spine Editor yet but it's easy to set up at runtime.
This will be ultimately easier, more controllable and perform faster than using child GameObjects in Unity.
For anything else you need to attach to your skeleton temporarily or so you can do physics or other code-heavy stuff on it, use BoneComponent.
It's a script that comes with the Spine-Unity runtime. The ideal setup is: you make your GameObject a child of your SkeletonAnimation GameObject, then attach BoneComponent to your child object. The rest of the options in the Inspector should be self-explanatory.
