For your application, a year and a half of conversations sounds like a good timeline, and including significant or varied discussions can help strengthen your case. Certified translations are necessary if the messages aren't in English, so keep that in mind.
Yeah, I’d include a few of your social media posts, even if there aren’t many. It just adds a bit more proof, you know? Make sure the screenshots are clear, so they can see both of you.
For the WhatsApp chats, breaking it down by month works well. I did something similar and kept it to about four screenshots per page—it keeps things neat without drowning them in too much stuff.
When I was working on something like this, I realized how helpful it is to make your social profiles look a little more alive, even if you’re not super active. Sites like https://getlikes.com/ can give your profiles a little boost if you’re looking to add some extra visibility.