These are just what I'm thinking, so please don't take them as legal advice.
Q1: You can wait for AOR and then submit a webform, which is what IRCC and many consultants would suggest you to do. However, I think you should fill out the webform now, even if you don't have your application number as if later on IRCC says that you didn't try to fix your mistakes, you can use the reference of you submitted the webform, but it was not processed, as an excuse. It doesn't hurt anybody if you fill out a webform now without putting in the application number. Most likely, IRCC will answer by wait for AOR, but I strongly recommend you to play SAFE.
Q2: Unfortunately, that's a big mistake. I hope IRCC will send everybody an AOR first and then process their applications instead of having some kinds of completeness checks, which I doubt as many people said this new program doesn't have a completeness check. However, we don't know how things will turn out so all we can do is prepare for the worst and hope for the best. I strongly recommend you to call IRCC to ask what you should do. Otherwise, you would also have to wait for your AOR as many people out there, who also made mistakes like you, have to do right now.
Q3: Yes, you can. However, I don't know how long have you worked at your previous job. If it's a few months job, then before leaving, I STRONGLY recommend you to get your reference letter, copies of payslips, copy of contract (if possible), T4 and ROE I think you can get them online. Those will prove to IRCC that you had worked at that place. Also, when you start your new job, get a reference letter or letter of employment ASAP, then submit it once you get your AOR. Make sure you keep IRCC posted about your situation ( I mean all the factors that required for your application) to avoid any delay.
Please do not take my advice as complete truth as this is based on my experience of dealing with submitting application and IRCC.