There is now a default assembly workbench. You don't need it for this. It is mostly handy to verify your design.
Assuming endless possible values: set up a spreadsheet, define an alias (top right) for the relevant values, and use that in your sketches and extrudes.
You could model the various bodies in place in the right orientation and make do without any assembly as there are moving parts too. The new assembly workbench is nice to use though so it's worth trying it out.