Greece is yours if you want it. We had a player for it so look up the turnposts of
@Pirx so you can get an idea of what direction he took Greece in, politically.
Also the Copenhagen Conference is of some relevance to Greece with regards Crete.
He's hedging his bets.
Perceptions are just about as important as the reality, sometimes moreso. The Duke is under no particular compulsion to accept a foreign throne, especially if it's one he thinks he cannot hold.
Quite the contrary, he's well within his rights to want a better picture of the situation and possibly some manner of gesture to
I thought on where Charlotte went and come to think of it, Austria was only her historical destination because of her attempts to raise support for Maximilian's regime so I think you are right, Belgium would be the better choice in this instance.