Starting with just an action, there's no real 'order' to it. You will have to amass and assemble all the various parts before you will have an operable rifle. that said, I would start with getting a barrel and barrel nut. If there's any metal work that will require a smith, that will take the most time so get the barrel and any work that it needs to have done going.
From there you will need a stock, bed the action into the stock. You will also need a trigger.
While all of these projects are going, you can be researching and ordering rings and bases for your scope.