Hi,
Not sure If I understood the problem correctly, but let me try, As you mentioned you want to download the label, I hope you are talking about the external APIs so the answer is Yes, you can directly consume those API with NAV using Json or XML response or methods.
Also for your 2nd question if I am right, you want to connect directly your GL balances or GL entries, I would say NO, please create a separate PAGE to show them what they required or elaborate it more so that I can answer.