For custom analyzer and custom token filters you can check:

https://github.com/VirtoCommerce/vc-module-elastic-search/blob/6271051b6d74ba67f4129dafad58d165028ff637/VirtoCommerce.ElasticSearchModule.Data/ElasticSearchProvider.cs#L389


Aggregations and buckets usage can be found here:

https://github.com/VirtoCommerce/vc-module-elastic-search/blob/dev/VirtoCommerce.ElasticSearchModule.Data/ElasticSearchRequestBuilder.cs

https://github.com/VirtoCommerce/vc-module-elastic-search/blob/dev/VirtoCommerce.ElasticSearchModule.Data/ElasticSearchResponseBuilder.cs