Concurrency support: more than one client posting or reading to/from speckle

Hi,
Can I get some clarifications regarding the below doubts.

  1. Concurrency support: more than one client posting or reading to/from speckle under one USER ID?
  2. What is the underlying DB ??: Mongo DB?; I believe it is PostgreSQL. Correct me if I am mistaken.
  3. Is it possible to upload glTf object into speckle server?