Re: your concern about not having many pictures, we didn't either. I included a couple random pictures from date nights and family events, like you said, but those kinds of things aren't as strong as evidence like others above have mentioned. I think officers are generally understanding that when you're applying for AOS from a K1, the initial packet may be a little sparse. It is really hard to get established financially before the EAD comes; we basically weren't able to do anything without that.
What I did was send in anything I had to start with, and then once I had the NOA and online access, I started throwing everything onto the Unsolicited Evidence portal. As we started a joint bank account, collected mail in both our names, added him to things like health insurance, car insurance, bought him a car with both our names on it, etc, I would upload the evidence there. It created an ongoing narrative of things we were doing to establish our life together as soon as we were able to, and then the officer had access to all of it when we were at the interview. During the waiting period we took a vacation so I uploaded some pictures from that as well to show us continuing to have a social life together.
I know it's nerve-wracking but, seriously, don't overthink it. Follow the instructions to start and then upload the evidence as you get it. Your relationship is in good faith so there's no need to struggle to fabricate things. All the things you'll collect are things you'd be doing anyway as a married couple starting a life together.