Sorted!
Got the front page to only show the most recent content by adding the following to my .eleventy.js file
eleventyConfig.addCollection("front", function(collectionAPI) {
return collectionAPI.getFilteredByTag("posts").sort(function(a, b) {
return b.date - a.date;
}).slice(0, 5);
});and then the loop in index.njk is
{% for post in collections.front %}
{% include "homeplate.njk" %}
{% endfor %}