CJ,
If I were to build these pieces, I think I'd opt for the bandsaw route. That would certainly work for the seat slats, front and rear stringers, and the armrests on the Weatherend piece. However, for the crest rail on my benches, I might have to laminate a blank. Same goes for the circular piece at the top of the Weatherend back. There are commercial adhesives that will work for outdoor applications; I've never used them, though.
Hope this helps.
Best,
dh