I answered this in the other thread, but just in case:
1) You don't need to, but you may file a G-1145 - yes, it is OK that it is expired. Bear in mind that USCIS does not always send you an email/text even when you submit this form, so don't be alarmed if you don't hear from them. And/or it may take a while, sometimes up to 3 weeks.
2) The affidavits are explained in the I-130 instructions (https://www.uscis.gov/i-130) page 3, item I -- it is just one example of what you can submit. You need to mix/match per your specific circumstances. Photos with friends/family are good evidence too.
3) That is fine if you don't have photos of the ceremony, as long as you overall have good examples to demonstrate it is a genuine relationship.
4) You won't file the I-751 until two years after your spouse enters the US with her immigrant visa - that too, it will only be needed if at the time she enters, you have been married for under two years. If the marriage is under two years, then she will be admitted with a conditional permanent resident card that is only valid for two years. In the 90-day window before the green card expires, she will need to file the I-751; you should look up the instructions and current fees at that time as they may change.