I\'m pretty familiar with the capabilities of ElasticSearch and its benefits, but this is the first time I\'m getting my hands dirty building an index. So I\'m eager to get
First it is worth noting that mapping types will go away in the next ES release (soft deprecation in ES 6 and removal in ES 7).
Now whether types go away or not, it is still possible to use a single index, however you'd increase sparsity since only 30% of your fields are common and that should be avoided at all cost.
So, I'd say that your multi-index approach is the only one that makes sense given the nature of your data.
Additional information worth reading: https://www.elastic.co/guide/en/elasticsearch/reference/master/removal-of-types.html