Minecraft wiki entry for Pumpkin_and_melon_farming, associated text: To speed up collection, place ice blocks under the watercourse.
The farm can be lit from within by glowstone as shown, or much more cheaply by jack o'lanterns. Unfortunately, you can't place a jack-o-lantern directly onto a piston, so if you need to put temporary blocks in place of the pistons, put the jack-o-lanterns on top of those, and then replace the temporary blocks with the pistons.
The pressure plate can be replaced with a hopper or two, leading to a chest or two south of it. Then, the Redstone can be triggered with a switch anywhere along its length. However, a sufficiently tall farm may produce enough goods to overwhelm the hopper (750 items—call it a dozen stacks—take 5 minutes to absorb, so additional stacks may expire. Twenty or so levels of melons could do that, or most of a hundred levels of pumpkins).