West coast route or east coast?
Photos of our trips to Tassie are posted
here (Western Explorer 'Edge of the World Tour') and for the east coast
here (Family tour 'Tasmania in thongs') and
here (Central Plateau & East Coast Group Tour). You may find them useful.
The family tour down the east coast was with my wife, 15 yo son and 13 yo daughter. We rode from Devonport to Hobart via Scottsdale, St Helens, Freycinet, Maria Island and Port Arthur in about 2 weeks. My daughter announced her runners were too tight on day 1 and rode almost the entire tour in her thongs, including a 100km day to get to Freycinet. So your plans sound entirely feasible.
Both son and daughter have later done both the grueling Edge of the World Tour with headwinds and huge steep grades, and the 3 week Central Plateau & East Coast Tour, and enjoyed themselves.
Riding bikes in traffic - what seems dangerous is usually safe; what seems safe is often more dangerous.