It can. Mine took around close to 21 months end to end. My case wasn't an exception. Some waited even longer.
There is a reason why USCIS is issuing 48 month extension letters.
500/1000 GBP ain't going to cause the headache. You only need to report 10000 USD or more going through your foreign accounts to IRS. If it's below, not much to file.
You can book cancellable / flexible tickets, but ideally you should book flights after visa and passport in hand.
How do you know you won't be placed in admin processing?
No and no.
Whatever vaccines you are missing are going to prevent you from adjusting status. You simply won't get green card unless you bring paperwork from civil surgeon saying you met all criteria.
It's ok to be worried, but as long as the father is a eligible joint sponsor, it should be OK. Sponsor should be a US citizen or US LPR, so your parents cannot help much
Focus more on covering the ongoing events.
There's not much value providing 10 pictures from the same day. Give 10 pictures from different days or occasions.
Visa is always best.
Technically, as a US Green Card allows entry to Mexico, but with mixed success.
Make sure to bring marriage certificate to explain name difference on passport and GC.
Yes, it's almost guaranteed that some people who filed after you will get approved before you.
Also a paper applicant filing after you with I-912 may get approved before you.
This is not a strict line where everybody gets adjudicated in order of filing. There's many factors and each case is unique.