Carpenter here whose build many fences/gates: redwood (cedar) is EXTREMELY weather resistant and has very little expansion/contraction, which is a good thing. Its the reason Cedar is used for siding, shakes, and decking. you shouldn't have any problems with it weathering down anytime soon.

Gate looks great, only nit-pick is the non-matching hardware but it w/e.

Little tip for board spacing (you might've used it and i overlooked and missed it) But the thick end of a speed-square is 1/4 inch thick and makes a great spacer.