1) yep - just keep "ExternalData" elements at the top of the json, e.g. <maplink>[ {"type":"ExternalData", ...}, {"type":"Feature", ...}, ... ] </maplink>
2) yep. There was a bug in the previous releases that has been fixed now (its on the deployment train, should be available everywhere today or tomorrow). You can have "properties" as the top level element of both "Feature" and "ExternalData" elements, with all the styling information. Also, Wikidata query can also return the same properties. In case you define properties on ExternalData and return it from the query, the properties will be combined, with the ones from Wikidata overriding those defined locally (per item).
Any help with documenting this is welcomed :)