Not sure what a "Cloud Engine" is seems to be a google term. but it could be. The devil is in the detail of your requirements
Collecting of data would be done by some other process, generally you do not want to write directly to Elasticsearch from the Wild of the internet. So some type of collector, (webserver, with php, java which write logs or "Proxies" the request to Elastic would be highly recommended
don't know what that means but sure once the data is in elastic search, you can query it with Zeppelin or Kibana
Yes very scalable,
If you can write the search you can display data in all kinds of ways. Kibana provides a good Generic and semi detailed view, but True analytics usually need to processed and munged spark/storm/hadoop, Which Elastic does interface to.
I would recommend you contact Elastic Sales rep and have a conversation with their Sales engineer. It is too difficult to give you an opinion based on such general details but I gave you some basic thoughts
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