What is most appropriate way to do this for my own schema?
It seems that you are trying to capture some specifications for electronic devices. In this case, you can then use plain OWL, this is one of its use case. You just represent the types as OWL classes as mentioned.
Should I use (a subset of RDFa)?
RDFa are meant to be used inside HTML documents for search engines to process, so I don't think it suits your case. But anyway: RDFa is just a framework to annotate content, so you could perfectly annotate HTML content with your XML types if you want a straightforward solution.
How do I go about incorporating this into my own schema such that it validates?
OWL ontology validation is done via a reasoner, if you use a tool like Protege you have would have a platform to edit and create your OWL ontology as well as to use the reasoner.
If you include some snippet of your XML and pseudo-code of what you want to achieve I could provide a more detailed answer.