1. No difference if both the parties in the joint account are dependents (spouse /partner) and applying for PR.
2. I remember having read CIC says if it is joint account, "should be with the accompanying dependent applicant (spouse/partner) for PR"...So if spouse is not traveling, even that joint account doesn't qualify, unless you have an affidavit showing the percentage share of ownership of the two, with both signed and notarized. Still, the minimum required as Settlement Funds for evaluation will be based on FAMILY SIZE including all the dependents, accompanying or not.
3. & 4. I don't have information.
Request other seniors / first hand experienced forum members to share.
all the best!