If I did the work myself / paid for the materials myself, Do I need a Notice of Commencement?

Generally, no - when an owner does all of the work themselves, there's no need to file a Notice of Commencement. After all, Notices of Commencement are really for the protection of owners, contractors, subcontractors, and suppliers on projects where there will be multiple parties working on the same job.

When there are no contractors, subcontractors, or suppliers, there's no risk of a third party lien claim (or really any payment issues). Thus, filing a Notice of Commencement probably doesn't make much sense.