Actually, I'm pretty fond of Usoppe's pic. Mostly her hair, and the fact that she finally wore a shirt under those overalls (soooo uncomfortable without one DX). It'll be harder to give her post-timeskip muscle, though she'll look really good if it's done right. Also, being female would probably only exacerbate her inferiority issues pre-timeskip, though it would make Sanja (what I call F!Sanji) cheering her up that much more touching.
I think maybe the problem with Luffyko's (man I don't like that name. Sounds awkward) picture is her lipstick and maybe her chin. She wouldn't wear lipstick, and her chin might be a bit too rounded.
F!Zoro's pic is... pretty much indistinguishable from her male pics. Which was part of the point, I'm sure. The change in facial structure (especially the jawline and mouth) is subtle enough that unless you're looking, you don't realize the difference. But once you do, it's really nice.
F!Sanji looks fantastic, as always. I already reviewed your color version of her pic here, so not much more to say about it.
Thanks on the Usoppe compliment. For some reason she's hard for me to do well consistently. I'm having the hardest time with her timeskip design, too. Grr. But yes, the t-shirt is non-negotiable for me. I always liked the shirt on guy-Usopp too, I wish he'd worn it more.
Yeah, I'm just not happy with that Luffy picture at all. Bleh.
I really, really like having Zoro be pretty much the same from male to female, save for the changes in bone structure and musculature and whatnot. Making Zoro traditionally feminine doesn't feel right to me, the same with Luffy. No reason I can think of why they'd have to change, either.