Yes, it is totally fine and, I would even say, preferable to use the http library. You still need to manually populate the http requests though, even with the library.
 No need to remove your debugging output for the submission, our grading setup will ignore it.
 Yes, it is normal :) We have locked the master branch for us to be able to push updates to the the tests (as we did for the integration tests) or generally the code base without having to merge. Perhaps not a perfect solution but it seems to work. And yes, it is totally fine for the submission.