Sounds like you've got a great trip planned there.
Having lived on the N.W. Coast of Tas for 20+ years, I miss it so much this time of year. Esspecially as all my mates are wheelin on the west coast and ringing me every day to tell me what I'm missing out on!
When you head to Arthur River and further down the west coast toward the Pieman you'll come across quick-sand and fairly fast flowing rivers to cross on the Sandy Cape beach (13k's long). Make sure you cross the rivers low (near te sea) not up high. If there is local guys about, take their advise. If I had a dollar for every vehicle thats been lost down there!
There is on way in, and one way out. No support, no tow trucks. You'll never get to the Pieman from Arthur River and back in one day. From the Interview River to the Pieman is very extreme. Really, you prob shouldn't tackle that part. Be sure to get a "permit" from the parks office a Arthur River. Its free, but if your caught without it- big fine!
The permit also states that no travel is allowed past the Interview, although they will never catch you that far down!
Have an awsome time in Tassie, I'll be heading over there this time next year for a wheel. Planning on doing the Jambo, then sending the Jeep to Tas on the Spirit then flying back to WA until early December. Then Fly back to Tas to "tie the knot!" and of course, wheel the west coast!
Once again, have a great time, safe travels and merry xmas!