I've always shied away from the P40E because I foresaw this problem with the stock nose art. However, some folks here have done skins successfully, so I'll defer to them on how they got around it. I can, however, help with some of your other problems, or at least give you the bad news....
As to the different parts of the plane having different-sized pixels, that's an unfortunate fact of life, especially with the planes with skins and models held over from AH1 and not brought up to AH2 standards

. That includes the P40E and basically every other plane in the game except the P51s, P38s, P47s, 109s, spits, FWs, the Ki84, the B24, and maybe a few others I've forgotten. HTC is gradually redoing all the planes to the new format, which will make all skins done for the old versions obsolete. IIRC, the B17 is next on the list. Thus, almost all skinning work these days is being done on the AH2-format planes, so as not to have one's work destroyed in relatively short order.
To post your progress, you have to upload the pic to webspace somewhere. Then, you put a link to that in your message using special HTML-ish codes this forum accepts. Look up in the upper left corner of the screen when you're typing in a post, and you'll see a link that says "vB Codes [help]". Open that and you'll see instructions for posting images and doing lots of other cool things in posts.
Also, be sure to get the skin viewer tool. This enables you to see the skin on the 3D model with MUCH better control over your view of it than you get in the game, and it also loads much quicker. Plus, you can move the controls and gear to make sure you've got all their lines in the right place. I don't remember the link offhand, but you can search for it. The only problem with the viewer is that every time they patch AH2, it doesn't work with the new version, and you have to wait a week or so before they release the next viewer version.