I think a grammarian would say its determiner there. But why do you care?

That looks correct although you could put a “his” before creative work. Used to hold means - no longer holds but previously did. So I take it that is not what you mean. Would always hold is an alternative, slightly more artistic way of saying it. The difference is it suggests a degree of future movement, it’s quite subtle. As if it puts the reader in the time you are talking in and moves forward across the relevant period. Held is just simple past, the term always qualifies it. In this case you could use either and it just depends on the mood you are going for

It isnt idiomatic, but it makes sense. Maybe you could say - she has a scientific enthusiasm and verve for knowledge. We don't usually combine the word verve with another word, but i do not think it is technically wrong to do so.

It is the difference between this and that. Meaning an abstract reference versus a reference to something that is right in front of you - "ostensive" . It is technically wrong to use ce about something abstract, but of course like in english people break these rules. But dont worry too much just remember if its in front of you then usually ce and if its not usually ca. And pay attention to what people actually say. One exception is that people will show you how to so something and often say comme ca.