Form N-400 part 1 B clearly asks whether you have been LPR for past 3 years, married to US citizen for those past 3 years & spouse has been US citizen for those past 3 years.
2 years 9 months is early filing requirement for you BUT you still need to fulfill requirement of spouse being US...
USCIS ports priority date automatically when subsequent I-140's are filed. If your employer or attorney brings to USCIS they will issue corrected oldest priority date.
Only in circumstances where fraud or misrepresentation is present USCIS does not ports priority date.
I believe you filed derivative employment based I-485 & missed out mentioning details on 3.a on page 3 & 9.a on page 4 of I-485. If that is the case your only luck is to wait until future months visa bulletin make your priority date to re-file I-485. I don't know if nunc pro tunc...
I believe you should be OK to stay outside of US until re-entry permit expiration even if it ends up more than 2 years provided you should be done with biometric & depart US
I am quoting Vietnam US embassy "If you have been issued a Re-Entry Permit, which applicants must apply for while in the...
If you move to new employer after 180 days of I-485 pending you are covered under AC21 portability provision meaning you don't need to do PERM & I-140 again. You can file I-485 supplement J whenever you are called for employment based interview
Big question if you are not retrogressed country like India or China your I-485 interview will be scheduled very soon and probably should be adjudicated soon. In that case it would be redundant to apply H-1B. Keep in mind you can file for H1B while pending I-485.
In case you choose to spend more...
In that case opt for consular processing. New employer when they file H1B have them check under I-129 Q.4 a Notify the office. By following this approach you can have H1B approved & attend consular interview get H1B stamp & re-enter USA based on new employer's H-1B
Effective 01/01/2021 USCIS/DOS is no more allowing to file I-485's based on date of filing. It has to be based on Final Action Date. I believe this might help you in your understanding to file I-485 for your spouse should the need be. This is in regards with employment based I-485 filing.
OK. So if I-539 was timely filed, he or she will be under period of authorized stay until it is adjudicated from US attorney general . I believe you are OK to file I-485 without having the need of invoking 245K