I just completed my first proposal and I would like to know if I would receive any notification if it was rejected by the client or would I have to monitor the posting to see if the client hired someone for the job.
Viv: do NOT monitor the job posting.
Do NOT think about that job. Submit your proposal and forget about it.
IF the client wants to talk to you, you will receive notification through Upwork messaging and email. Only then should you continue to think about the job.
Yes on both account. You will be notified if your proposal was rejected, as well as if a client hires a freelancer and closes the job. A client can also hire a freelancer and leave the job open, without rejecting your proposal, in which case you can find this information by checking the job post page.