Are there any enterprise features on ECE that are not available on ECK?
ECE has a UI as you noted in the next question to create clusters, update clusters and monitor clusters. Also certain features work differently in ECE such as setting up a monitoring cluster now can be done with checking a box and selecting the cluster to ship logs/metrics to. In ECK all of this can be done through the CLI native to k8s (kubectl command line). There are no other features that are part of ECE not present in the enterprise tier in ECK.
Does ECK have a similar UI to ECE for cluster creation and management?
As I note above not yet.
Due to the way ECK is built (it's an operator running on k8s), it has a native k8s experience in order to create and manage elasticsearch clusters as well as other components (kibana, apm, agent, beats etc).
Let us know if we can help with any specific features you might be interested in.