Hello, Derc!
You asked if there are rules on AARs. The rules which apply are the TWC Terms of Service. There are also the rules of our competitions, if you enter the Monthly After Action Report Competition (MAARC) you'll find the rules in the OP of the submissions thread.
There are also informal, unwritten rules, such as:-
-> If you want others to post friendly responses on your AAR and Creative Writing, post friendly responses on other people's AARs and Creative Writing.
-> AAR updates (and responses by readers) go on your AAR thread, discussions of writing (and questions about writing) go in the Writers' Lounge (either on this thread or by starting a new thread in the Lounge)
-> If you want to advertise your AAR, you can do this by posting on the Advertising Board (here in the Lounge), by adding a link in your signature (when you have 25 posts) and by entering Writers' Study competitions. There's also currently a one-off Write an Advert competition happening. When you have posted the OP of your AAR, so that you have something to link to, you could enter this competition if you'd like to. (If you'd like to know more about adding signatures and similar things, I recommend Shankbot's Unofficial Guide for New Members.
AARs which are mainly images are welcome. The size of your image looks okay to me. Having said that, "dozens" of images - like a very long text post - could make it harder for readers to keep following your AAR. I suggest thinking about the time that it will take for someone to read one of your chapters, and imagining a stranger asking you to give them that amount of time.
There is a gallery function on TWC, although I didn't discover this for a very long time! To find it, select 'My Profile' (in the top right hand corner of the screen) and 'Albums' (from the list on the left of the screen). Create an album, upload images and save them. Then select an image you'd like to add to a chapter and copy and paste the code into your AAR post. Select 'Go Advanced' and the preview post option to check that the image is displaying properly before posting.
You asked about copyright. While I'm not a member of Moderation Staff, so I'm not someone with official authority to interpret the site's rules, the TWC rules say that the "Substantial use of copyrighted material without permission" is not okay and that "Examples of acceptable uses would be brief quotes, fan art, signature/avatar images, brief video clips (e.g., YouTube), screenshots, or reasonably limited decorative images in a mod". Screenshots, included screenshots we edit (for example to add arrows and labels showing the movement of armies) are okay.