You are correct that the Periodic Statement requirements apply to closed-end consumer credit loans secured by a "dwelling", and that there is a small servicer exemption to the Periodic Statement requirements for those that qualify.
You are also correct that the ARM disclosures are applicable to closed-end consumer credit loans secured by a principal dwelling, but remember that there is no small servicer exemption to the ARM disclosures. So even if you qualify as a small servicer, you need to comply with the ARM notice requirements.
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My opinion, take it for what its worth. Opinions expressed are my own and not those of my employer and are not legal advice.