Yes, now I can access my_elk_server_ip:9200 which shows:
{ "name" : "ELK_1st_node", "cluster_name" : "ELK", "version" : { "number" : "2.3.3", "build_hash" : "218bdf10790eef486ff2c41a3df5cfa32dadcfde", "build_timestamp" : "2016-05-17T15:40:04Z", "build_snapshot" : false, "lucene_version" : "5.5.0" }, "tagline" : "You Know, for Search" }
For your 1st question: sorry I don't know how to set the logging level to 'debug' in config file.