#5 is a bit of a double-edged sword, isn't it? All RNGs that I know of would require a shared seed value, and with procedural generation, you can effectively path any/everywhere in parallel.
You can always leave some crucial part or procedural generation on server-side too and impose some limits on how client can use API to it. E.g client might do any kind of heavy lifting (generation of terrain, etc), but code that handle important stuff (e.g PvE enemies, rewards) could be stay on server-side.
