My understanding is that a lack of robots.txt should be fine and the lack of a sitemap.xml shouldn't be too troublesome as long as there is something linking to

My understanding is that a lack of robots.txt should be fine and the lack of a sitemap.xml shouldn't be too troublesome as long as there is something linking to your site and all pages are linked from somewhere on your site (the sitemap helps search engines find all the links in one place but you have a nav bar or an article list that should work similarly, but you can give a suggestion to search engines about how often they should recrawl in your sitemap, which I don't believe you can influence any other way).