You can apply stain over peeling stain, but it’s not a good idea. Your old stain will get in the way of your new stain bonding to the wood, so you’re likely going to see the same issue again shortly after application. Your best option is to sand off the old stain and clean the surface thoroughly before applying new stain.

Satin paint is generally considered a better choice for woodwork—including trim, baseboards, cabinets, and doors—than flatter finishes like eggshell or matte. Its soft sheen enhances architectural details and stands up well to frequent cleaning and daily wear. Compared to eggshell and matte finishes, satin is more durable for high-touch areas because it is less porous and doesn't absorb dirt as easily. Matte finishes, in particular, are prone to scuffs and are harder to clean, making them less practical for surfaces like doors and cabinets.

Whether to brush or roll stain on wood depends on the project and your preference. Brushing is ideal for smaller, intricate areas and offers more control over the application, ensuring thorough coverage and penetration into the wood's grain. 

Conversely, rolling is efficient for more extensive, flat surfaces and can save time. However, it is not always the best fit for textured or uneven wood. Some projects may benefit from combining both methods, using a brush for detail work and a roller for broader areas. Ultimately, the choice between brushing and rolling depends on the specific requirements of your staining project.

Always wait until the morning dew has dried before you stain your deck. The stain needs a fully dry surface to sink into.