I usually pick my Japanese cukes while they're still fairly slender, about 1 1/2" or so. If they're bigger than that, you can always slice them lengthwise and scoop out the seeds (if you care), of course.
You can scrub the prickles off or peel them. I think due to our relatively low humidity, our cukes tend to develop tough skins, even varieties that claim to be tender. I sometimes find ones that I consider tender enough to eat, but I usually peel mine, especially the prickly ones.
Be sure to taste test near the stem end for bitterness. These heat waves have not been kind to our cukes.
Thanks! I immediately went out and harvested four, to add to the one Alice snagged against my wishes this morning. Luckily, they don't seem to be bitter, and the prickles come off pretty easily under the tap -- but you're right, they're better peeled. The number of cukes in our future is a little frightening, but Alice loves cucumbers (she ate most of a large cucumber this evening while we were making dinner), and we all like pickles.
Heh, in the summer I make a *lot* of cucumber salads. It's amazing how many variations you can come up with if you put your mind to it: vinaigrette, cream, yogurt, herbs, several Asian styles (fish sauce, soy sauce, sesame oil), lightly pickled, Greek (feta & olives), etc.
Here's a simple but odd cuke salad that I grew up with: thinly slice the cucumbers and salt them. Drain if they generate a lot of liquid. Add a little milk or half & half and a generous grinding of pepper. The big treat with this is the salty peppery milk left after all the cukes have been served. My mom would set out separate small salad bowls on the night we had this for dinner, to keep the liquid from running all over the plate. These days my dad adds some thinly sliced onion to the mix, which he says is more authentic. I believe him, but I still adore the simple, non-onion version.