All financial and employment documents must meet the 28 day rule, and the most recent document in a series (i.e., payslip or bank statement) needs to be dated within 28 days of the online application submission date.
And just to confirm also, that these documents must NOT be older than 28 days from the application. Does that mean that if I applied on the 27th online, that any documents which need to be dated could be no older than the 29th of January?
I am not sure where you get the 29th of January?? If you apply online on 27th Jan, then your most recent financial/employment document can't be older than 30 Dec.
Priority (NOT Premium) service doesn't guarantee a faster decision time in any way. The difference between "priority" and "premium" is that "priority" service gets your application put ahead of the non-priority queue for processing. "premium" services are extra (IMHO, unnecessary) services available at the VAC like lounge access, SMS notifications, courier service, etc.
You just need a letter from your parents and the land registry document (which you can get for £3 online) which proves your parents own the property. You don't need a Property Inspection Report unless you're living with other people and there's doubt as to whether or not it might be overcrowded. You can also provide a recent mortgage statement if you want but it's not strictly necessary. You should also provide a copy of the property owner's passport bio page.
Your partner should plan on bringing all of their supporting documents to the biometrics appointment, even if they have uploaded them yourself beforehand.
If you weren't asked to provide barcode separators, you don't need to provide them. It depends on the VAC
You only need a plain photocopy of your UK passport bio pages - It doesn't need to be certified and it doesn't need to be a full copy of their passport