Well for the point no. 2 where you are getting an error related to ssh, you must be forgetting to use the keywords "ansible_user" and "ansible_password" in the inventory file of that system because ultimately in ansible we login into another system mentioned in inventory file for config. purposes via ssh from the controller node.
Also, there is an another option available as well to do this by generating a ssh key and copying it to the system in inventory file by ssh-keygen and ssh-copy-id cmds.
Hope you find this helpful!