You might be well aware of this, but it's always good to cover for anybody reading. A lot of the typical woods used for marine and outdoor use, Teak, Mahogany, and especially Cedar, can cause a nasty allergic reaction, when sanding. Oddly, I get it after a day of cutting fir lumber while framing. Masks and cheap respirators are helpful, since you don't need to discover that this is a previously unknown personal health issue, about the same time you think, "damn, it's really getting hard to breath"
The treads should be beautiful. I redecked my parents front porch with clear Mahogany T&G almost 20 years ago. It's somewhat under cover, and faces north. It's coated with spar varnish, and it still looks great.