I can't speak for Unity part, but in regards to props you can use purchased content in your games.
As per what version to buy, I would purchase Character Creator Pipeline, with Headshot Plug-in. I used to always purchase characters, since Headshot came out I haven't purchased one.
As for use in Unity, most props have an Export license and a regular license. For you to use in IClone, you just need the IContent license.
To export to Unity you will need the Export license.
Maybe that answers some of your questions. Maybe someone else can answer the Unity part specifically. I should learn it, but I do not code games.
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