is nirvana - just whatever a Buddha wants? Suppose Dave is a Buddha.

Does he want to be a Buddha? 

Will he get what he wants - forever ?

Does it matter ?
Does he want to be a Buddha?


I think it's usually expressed as a negative:


Life (or the experience of life) is unsatisfactory when you're not a Buddha; many examples of its being unsatisfactory include poverty, illness, death, separation from people and things you love, inability to have what you want, inability to keep what you have, failure to do what you want to, etc. (sorry for all that bad news! :-) That's the so-called "first noble truth".
This dissatisfaction is caused by desire: I want to live forever! I want all my friends and family, and everything I like, to live forever! I want no pain, no sickness, for anyone! Lots of money! Endless paradise! Never anything unpleasant! But I can't have any of these things and so life is unsatisfactory. That's the so-called "second noble truth".
This dissatisfaction (and desire) can end. If I stop wanting things that are unreal, stop wanting to keep things that are impermanent, then I'll stop finding life unsatisfactory. That's the so-called "third noble truth".


So I think that the Buddha knows (and teaches) that wanting (thirsting for) the wrong things (e.g. impermanent things) causes unhappiness. Dave no longer wants those things and is, consequently, no longer unhappy.


  Will he get what he wants - forever ?


Well, yes: for as long as he's alive. It's assumed that once he became fully enlightened then he will no longer (or not again) become unenlightened. Because being unenlightened means wanting the wrong thing, wanting the kind of impermanent thing that will cause unhappiness: and the Buddha knows better (is wiser and has more discipline) than to do that.

There is a bit in the literature where people asked what happens to a Buddha after he dies, and the Buddha says that's one of the questions that not worth asking.


  is nirvana - just whatever a Buddha wants?


I think it can be described as being liberated (freed) from the dissatisfaction which is caused by wanting or clinging to impermanent things.



So I started to answer: what the Buddha taught might be summarized as "the four noble truths" or as "causes of suffering, and his path or way to end suffering".

And I started this answer by saying it's expressed as a negative ("end of suffering").

But there's more to the teaching than that: joy; serenity; loving-kindness. Removing causes for suffering allows room for other, better experiences, more like the "getting what he wants" which you asked about. For example the Kimattha Sutta mentions words like 'reward', 'joy', 'serenity', etc.

I think that the Buddha also decided that a cause of dissatisfaction (which, he freed himself from) was views about 'self': views like "me" and "mine" etc.

According to the biography, once he became enlightened he felt compassion for other people who were still suffering, and decided to try to teach to them (in case, with the help of his teaching, some of them too could free themselves from suffering). And so he began to teach.

I guess we can say that that (i.e. helping to enlighten other people, other people becoming free and safe) was what he 'wanted'.