Yes you can associate assemblies on a sales order to a production order and then to order planning/planning worksheet which will allow you to then generate Purchase documents around the parts of an assembly. But it would be much faster to include that functionality directly in the Order Planning/Jobs planning lines. This lets you skip the production order step and go straight to the order planning window to generate Purchase Orders. This supports situations where you have more job shop requirements than straight demand/supply plan calculations.

Second point - include Purchase Quotes as a document task choice from Order planning module.