First of all there are several options to get to the places you mentioned.
1) bus or train schedules from Santiago to Chillan exist daily.
2) the same travel options can be applied for the Chillan-Puerto Montt stretch
(Be advised to have a look at the surroundings of Puerto Montt, Chiloe and
Puerto Varas before you continue)
3) Depending on the season (Dec-Feb.) you can take the land trip from P.Montt
with a car (or hike), with 2 ferry crossings, to Chaiten along the northern
section of the carretera austral. Although beautiful, it can be a bit difficult to
hike on this stretch, as traffic flow is low.
The alternative would be to take the year round navimag ferry
(www.navimag.cl) from P.Montt to Chaiten. This is what the people usually
do.
Once in Chaiten you have many things you can do.
a) visit the Pumalin Nature Reserve and the Amarillo Hot Springs.

go to Futaleufu by bus (not daily possible) and experience some wildwater
there
c) take a bus and travel some 450 kms further south to Coyhaique and the
General Carrera Lake.
Happy Travelling!
Joachim
http://www.chiletravelcontact.com