Hi @Elljames,
A warm welcome to the Bunnings Workshop community and thank you for your question.
Paint will not adhere particularly well to oiled timber, so painting first is the better option. The order I would advise is, sand, apply masking tape, paint, allow the paint to fully dry, apply masking tape again and then oil.
With any timber project, the most important step is to prepare the surface by sanding. Use 80 Grit Sandpaper, followed by 120 Grit Sandpaper to smooth and prepare the surface. Brush it down to remove any sawdust before proceeding.
Use painter's tape to delineate the painted sections from the oiled sections. Check out How To Prep Your Paint Job With Scotch.
Apply 2-3 coats of your chosen exterior paint, following the manufacturer's guidance on wait times between coats.
Once the paint has fully dried, apply the painter's tape over the freshly painted section before applying your choice of oil.
Let me know what you think and if you have further questions, please don't hesitate to ask.
Jacob
