What are the features of JMCF for Jira Cloud compared to JMCF for Jira Data Center/Server?

The primary difference between JMCF for Jira Cloud and JMCF for Jira Data Center/Server is the support for scripted fields; at this time, JMCF for Jira Cloud does not support scripted fields. See this page for a feature comparison.

Can I migrate from JMCF for Jira Data Center/Server?

At this time, migration from Jira Data Center/Server is not supported.

Does JMCF for Jira Cloud support scripted fields?

Not at this time. Scripted, or calculated, fields are planned for a future release.