as far as I can see the only thing you have that really warrants a circular buffer is the error logging. If so, why not store the rest in fixed locations and have a circular buffer for error logging only.
I'm not sure what you mean by the "rest" here.
As far as I can understand you you have things that always log, that is waht I call "the rest"

Basically what I've implemented (and looking for advice on) is a EEPROM based logging system consisting of a (convoluted) circular list of error entries and a header (head pointer, tail pointer, misc.) stored separately in the EEPROM in a fixed location. Is that the type of solution you mean?
No, if you try to make a "(convoluted) circular list" you will get into such a mess. Just take an example (and do not reply "that will never happen" it will). For illustration I describe a circular list that can hold 4 entries. example: you have an error #4711 that occur once an hour and you find the slot in your "(convoluted) circular list" and update the count to 567. then 4 other events come along and you have no entry for #4711 left so next tome this error occur the count will be 1.

I can not give you any advice re "what I've implemented (and looking for advice on) is a EEPROM based logging system consisting of a (convoluted) circular list" other than DO NOT.

Erik