It is a great question, Philski. I have the answers for you ready.
It is advisable starting the build log as soon as you start the actual model build, but it is not a requirement. It is just easy to follow the log from the beginning. There is no limit on images\photos, there is no limit on their size\resolution as well. The forum software will take care of compression, and will present uploaded images without sacrificing their quality. However, you can post up to 25 images\photos per single post. This is not the issue as we don't expect your build log will be a single post and you will have only 25 images.
I also would like to point out that most of our build logs, IMHO, are for other members or guests. The good build log spans many posts consisting of not only images\photos. Think of a build log as the story about your model development, the processes involved, and techniques you will\may use while building. It can be of great help to others.
Remember, we learn from each other, so don't delay, start your own build log of San Francisco II NOW! We are waiting...
BTW, Many thanks in advance.