Can I limit what goes into the recommendations as items only within the featured item’s collection?

While directly you cannot select items to recommend to your visitors, you have the option to limit the list of items, which Autocommerce can use to select from.

All you will need to do is change the recommendation type from Intelligent product recommendation to Category Best Selling and at the same time sort the products based on product types.

Here’s a quick guide on how this can be done:

https://help.shopify.com/en/manual/products/details#organization

And a Youtube guide as well:

Unfortunately we do not support Collection based Recommendation but only Product type based ones.