Are you able to elaborate on why you chose EAV over using something like the json1 extension of SQLite?
It was built on a single table that held the entity-attribute-value tuple along with some additional metadata like type information, whether or not the attribute was a pointer to another entity, and the cardinality of that relationship (one or many).
Relationships were walked via self joins and the eav columns were all indexed.
The difficulty with having all attributes be EAV becomes apparent when having to do multiple joins to fetch a single record type (what would be a “table” traditionally). Although this is manageable, the bigger difficulty I’ve found is synchronizing deletions of records, especially if deletions/insertions are done in bulk. Rather than just 1 transaction you have to do multiple delete/insert queries to also delete/insert the attributes and the values and they should be done in a way that doesn’t break key constraints.