H1B extension and H4 COS in parallel, when I-485 AOS is pending

My H1B and I-94 are expiring on Feb 15th 2021. My husband and I both filed I-485 AOS through his EB-1. My H1B renewal is in process and in RFE.

(i) If my H1B is denied, Can I apply for both H1-H4 COS and H1B 2nd application for extension(same company) in Jan 2021, prior to I-94 expiry? Which one should I apply for first?
Is there an advantage to applying for H4 COS first, followed by H1B Extension or Vice versa?

(ii) Can I file both H4 EAD (along with H1–>H4 COS) while there is another pending EAD application via I-485 AOS? Can one have 2 EAD cards (H4 EAD and I-485 EAD) at the same time and choose which one to use? I would like to use H4 EAD.

You can file as many applications as you want but the more you file, the complex it will get.

You can only have one status at a time i.e. either H1B or H4.

You can have both H4 and 485 EAD at same time.

Thank you @anil_am22
In my case, for Quest#1, is there an advantage of applying for either H4 COS first or H1B or vice versa?