You will need to show the exact dates in your reference letter, your travel history, personal history etc, it's all cross referenced very easily.
The vacation is okay if it's paid and approved and no more than 2 weeks a year.
Yes, just don't get lost with these vacation days and foreign experience, that would be a real misrep.
You should be good.
Don't put it off for the last day as well, that's risky.
No need to decline. If you still don't have a buffer within a 60 day period to apply, you can do it your way and submit a letter of explanation with your calculations.
To be in a common law relationship, you don't need to be divorced, you should have lived together 12 months without any relationships with your ex of course.
If you don't get any points for that, there's no use to put it in the employment history, it will just complicate your application, but no biggie anyway, your call. But you must fill in the personal history without any gaps.