AFAIK no reserved things - just make sure you ID partition correctly, as plain fdisk does something funny with it (like setting same ID for every type of partition).

Not so long ago, I had a headache trying to understand why N900 fails to properly use perfectly fine partition table, in particular, deny to use OptFS. It turned out, that some startup scripts (rcS-late?) "cleverly" identify partition meant to be Opt by... checking ID. That is, f****n ID - almost as stupid, as using labels for that purpose. As every partition has same ID, it wanted to use MyDocs (as first found partition with matching ID) for OptFS purposes, resulting in disaster. Setting correct Ids via sfdisk (without re-formatting, just changing IDs itself) fixed it immediately.

Other than that, no special requirements for OptFS, you may give it whatever labels, root reserved percentage, journals, etc. you feel fancy.

/Estel