It’s not optional. The one you obtained 18 years ago to immigrate to Canada is not relevant for US immigration.
If you can’t get it in time for the interview, you should attend the interview anyway. You will get a 221g pending the consulate’s receipt of the PCC. Your case will be in administrative processing. Expect extra time if you’re from a high fraud/high risk/MENA country.
This is not a good choice for a joint sponsor. I'd find another one, or figure out why the petitioner isn't doing everything in their power to qualify. Sometimes people have to explore getting a better/2nd job in order to sponsor an immigrant. Immigrating to the US is very expensive, as is living here.
I'd steer clear of claiming to live together if you are visiting as a Canadian. You could put "May 2024-present" or something, but again, the B privilege for Canadians is for visiting, not for moving to the US.
Has the lawyer explicitly stated that there will be no problem with her CCP affiliation? Because that is kind of a big deal to the department of state.
The CR-1 is a much better visa, primarily for the reason you describe - the ability to work and travel immediately vs waiting up to one year. Either option will not be quick, and will require AP due to the CCP membership. Good luck.
State rep cannot help anyone establish domicile.
Best evidence is job offer. OP, some people find they have to bite the bullet and actually move and start working ahead of the spouse in order to satisfy the domicile issue. Good luck.
I think sometimes it’s simply a case of someone needing to sign off on something, and they are on vacation or whatever, etc. I don’t think there is anything to worry about- just the usual summer slowdown at ol’ USCIS.
There is no fixed time allowed. Each border entry is at the discretion of CBP. They will stamp the allowed time in the passport.
Note that if you are attempting to “live” in the U.S. for 6 months each year, expect trouble and risk to the B visa.
Also- they will wonder how you can afford to do this, and you should know that remote work is NOT allowed.