For your #1 point our team has had great success using PlantUML for our diagrams. They can be easily output for slides or wiki pages, but it's all written in code so we can keep them in our git repo for tracking.
Two of the teams I worked on supported a couple thousand devs each. So going in I thought it would be everyone using specialized diagramming tools. But the majority did not. I don't do much architecture these days, but I've bookmarked PlantUML just in case and will check it out if the need arises.
