Hi there,
You can choose 2 options,
1) chrome Extension
2) VB Script
Advantage of VB Script is that it will run in background, but chrome Extension should have to be operated live.
And daily 400,000 is not possible, as each page takes time to load, then only we can fetch data, if you want you can run the same software on different machine or same machine with different indexing.
Lets chat to discuss this in details.