Afraid of overapplying

Hi! I installed a 16x20 KDAT pressure treated pine deck a little over 6 weeks ago. I’ve already purchased the RAD cleaner and Brightener and just finished staining my sanple boards (leaning towards the cedar - was surprised to see it looked more brown than the light walnut which had a slight orange tint to it). Before I purchase the actual stain, I’ve got a couple last-minute questions. First, how much stain should I need to cover a 16x20 foot platform deck (one coat)? Second, after looking at some of the posts, I’m a little nervous about over applying. I’ve never cleaned or stained a deck before. I used a paint brush to paint the sample boards (we cut one of the remaining boards into 2 foot pieces to use as samples and left them outside to weather alongside the deck. I used a little of the cleaner and a scrub brush to get the remaining mill glaze off first), but plan to use a staining pad to do the full deck. How do you know if you’ve applied enough/too much stain? Finally, for the cleaning, I was planning to use a sprayer and then pressure wash it off. Can I just spray it on and let it sit, or do I still need to scrub it to get the glaze off? Any other tips/suggestions? Thanks!