Gunmaaarrk,
As for tower 'choice'. All that really happens is they find the towers that need new staff and send the graduates there. They range from Capital cities to Class D and the Towers "formerly known as GAAP". One cyear you might get lucky and you favourite tower/city is on the list, other years: Alice, Broome and Launy!
*No offence to those that work there. Just having a laugh
As for Enroute -> Tower in 5 years? Join the queue, its about 20 years long I think.