In-place upgrade of cluster 1.9 to 2.3

Hi,
I know this is a no-no, but I'd like to give it a try.
I upgraded a test custer from 1.9 to 2.3 in my office, but now I need to do it on real servers in a web farm (ouch!).

I think that a node cannot join a cluster in 2.3, if the node contains any virtual machines. So the correct procedure would be to upgrade nodes and then import old machines in this sequence:

1. Upgrade the master node
2. Create the cluster
3. Import VM running on master in the cluster.

Then on each node repeat:

1. Upgrade node
2. Join cluster
3. Import VM from that node to cluster.

Is that correct? Can I import machines from a secondary node in the cluster with the "import" script?
I'm trying to minimize downtime so that I would like to import VM on each node as soon as it's running the new proxmox.

jinjer