What happens to the proposer of an edit when an edit is rejected? Are they notified?
Is there a limit to the number of edits a reviewer can reject?
They are not notified of rejected edits. There is a list of the proposed edits they did in their user profile, thought; that list first reported which ones were rejected, but it seems not to show that, now. They can always follow the links reported in that page, to see if the edit has been approved or not.
There isn't a limit for the edits users can reject, but there is a limit for the rejected edits done from a user; when the consecutive rejected edits are more than X, the user cannot anymore suggest edits for 7 days.