ETA big batch request limitations

I am required to subscribe to around 14K items,

using the code in ETA tutorial with combination of batch request, I was able to get roughly 600-1000 items, depending which items I request (short names or long),

is there a config parameter that can increase the amount I can send, and if the limitation is not in the API, then can I split the request on several threads and use same user, and if so, will it count as 1 use or the user or multiple uses ?