Model tweaks

Hi guys, thanks for developing this nice model. Here are some tweaks. 
Nice chatting with you Jarod :)
What's the motivation for changing the default to 3 years? Most bachelor degrees are 3-5 years with an optional extra year for honours. A large proportion of students at the ANU undertake double degrees (4 or 5 years) which factored into our decision to choose 4 as the default. I haven't got any data on the average degree length in Australia but my guess is that 4 years would be more accurate.