Weblogic domain and cluster creation with WLST
I eventually found the answer. I am posting here for reference.
Out of the 5 mentioned tasks, all can be performed with an offline wlst script. All of them have to be performed on the node where AdminServer is supposed to live.
Now, for updating the domain information on the second node, there is an nmEnroll command in wlst which hast to be performed online
So, to summarize,

Execute an offline wlst script to perform all the 5 tasks mentioned in the question. This has to be done on the node (physical computer) where we want our AdminServer to run.
Start nodemanager on all the nodes to be used in the cluster,
Start the AdminServer on the node where we executed the domain creation script.
On all the other nodes execute the script which looks like following.
connect('user','password','t3://adminhost:adminport')
nmEnroll('path_to_the_domain_dir')
I want to create a cluster with 2 managed servers on 2 different physical machines.
I have following tasks to be performed (please correct me if I miss something)

Domain creation.
Set admin server properties and create AdminServer under SSL
Create logical machines for the physical ones
Create managed servers 
create cluster with the managed servers

I have following questions.

Which of the above mentioned tasks can be done offline if any ?
Which of the above mentioned tasks must also be performed on the 2nd physical machine ?