James, it’s usually best to allow new wood to weather for at least 3-6 months before staining. You can use Extreme Wood Stain on the cedar railing and it will work fine. The Butternut color is a semi-transparent, and will last longer than the clear. For application, you’ll need a to apply with a brush. Make sure to cover the Trex as it will be difficult to remove any spills or drips. The consistency of the stain is similar to water and it’s going to be easy to have drips, so be sure to protect the deck sufficiently. If you do get any on the deck, rinse immediately with plenty of water and a scrub brush.