I do not think these distinctions matter in the standard at all - and I recommend using the term character encoding (which applies to all character encodings, whereas CEF/CES are Unicode specific), BUT we may want to specify the endianness of UTF-16 and UTF-32 to be implementation-defined.

Implementation defined, but consistent with integers. That is, U'\u1234' must be a char32_t with the value 1234. I am fairly certain we require this already. 
A library facility that decodes UTF32LE would operate on bytes, not char32_t.