1) There are two options here.
- You run the installer on Node 1, but it copies the installed files to all other nodes in the cluster, so all nodes have a complete installation of the software (Grid Infrastructure and Database).
- You perform the installation on shared disks, so one software installation is used for all nodes. They all mount the same shared disks. For very big clusters, this can save space, but I prefer not to do it this way.
2) There is never just one node with the clusterware, so this can't happen. See above.
3) If you are using Standard Edition RAC, then ASM is mandatory. If you are using the Enterprise Edition RAC option, then it is not. Some people choose to use other cluster-based storage, like NFS for example. You can use ASM on top of other cluster-based storage, but it is not necessary.