1. These are different products. Contact with you Sales Rep. to get help how to migrate. They would do their best to make your transition seamless.
2. You can purchase a license for e.g. max 100 concurrent host units. So yes, you can change hosts within the limit.
Dynatrace is a different product and so the licenses are completely different. You can work with your account team to see about how it can be converted based on your AppMon licensing.
A Dynatrace Managed license is licensed at the cluster level. You can have multi node clusters but can't for instance use the same license between multiple clusters unless you have uninstalled/unregistered it from the initial one.