Go to my site (link in signiture) click on the “Tools and Tips” button on the bottom of the page, see “The Basics of Weathering” then see “Salting and Raised Panel Lines” for advanced weathering. If you have questions my email link is on the site front page and you can email me directly - always happy to help
No … you use chalk pastels for this. Oil pastels are just a glorified crayon and will only clump up when you apply them to the model.
To apply, sand the pastel stick until you get some “dust”. Use a small course brush to apply to the nooks and crannies. Then use a fan brush to achieve an overall dust.
In answer to your first question, use both dry brushing and pastels to achieve the best results.