urgent: ask for help

My H1-B will terminate in late January and my new employer delayed the visa transfer and I may not have a new H1 right after the current ends.

So if I use EAD card obtained from I-485 filing, can I change back to H1-B later on? Will that hurt my 485 application?

If I want my current employer to cover my H1-B as taking unpaid leave, since there is no payrolls, does that hurt 485 application?

If I do not have H1B and do not have a job, how long is the time limit for such status? Does that hurt 485 application?

Should I let USCIS know if I change a job?

Now my situation is quite stressful, I appreciate your help.