I think that no matter how sound your application is, that the more proof the better. Of course, that should be tempered with quality over quantity.
What I've learned here is that CIC does not place as much credence upon samples from texting/messaging, as they are more susceptible to being faked. That said, I would include a couple from each week or month from start to finish, to show the continuity of communication. What I did was to actually categorize my evidence (chat logs, emails, FB screenshots) under a few different headings (Family Interaction, Relationship, Religion/Spirituality, Environmentalism - all topics that our relationship had roots in)). With each category, we wrote up a few pages describing each one, making references to specific pieces of evidence that we wanted to highlight to CIC.
However, what CIC likes to see are pictures, especially those that show family interaction. Again, what we did was to take the pictures, two or three to a 8x10 photo paper), and put them into Microsoft Powerpoint. Below or beside each picture, we wrote the date, location, who was in it, and a brief description about what was going on in the picture. Then we printed them off on our inkjet printer.
As far as your phone is concerned, go ahead and use the pics anyways. They may be smaller, in order to preserve the quality, but it's better than excluding them, especially if you have really good shots you'd like to present in your evidence. Ditto the ones from FB. There's no reason that they could not be copied onto a program like we used, and have a caption added.
For the letter, we had friends and family write some for us. I don't think it hurts at all. In our case, some of the ones from my wife's side were written in Bahasa Indonesian, so we had them translated. For a spousal sponsorship, translated letters do not have to be certified, but we went that route anyways. It cost us a few bucks more than we needed to spend, but it was money well spent if it adds to the strength of our application.
I hope this helps!
I wish I had pictures of his family and friends with us all together, but we will have more with coming visits.