There's an existing Howl's Moving Castle thread, but I'll answer a few of your questions here.
The coat is weird, of course, so I'd recommend making it. It's such a simple pattern that you might actually have trouble finding a good pattern to modify; either way, make a mockup first to see if it will fit on your shoulders well. Incidentally, the Triangle Coat (the pale yellow one with the gold trim and lavender triangles) is far easier to make, since you don't have to do the quilting. Quilting is not easy. You're REALLY lucky about the shirt; McCall's just came out with the PERFECT pattern to modify if you want to do the first shirt for the blonde-haired outfits. McCall's M4862
in View B with added ruffles where the yoke and the gathering meet would be so perfect it's scary. I'd probably make the cuffs bigger than the ones they have shown, though, but it is still gorgeously a good pattern for Howl. If you ask in the main Howl's Moving Castle costuming thread, I can help you if you decide to do any of the other outfits.
Earrings? Find green teardrop pendants (of do what I did and get clear glass pendants and cover them in lime green sharpie and seal them with clear nailpolish) and put a shiny red gem bead at the top and attach it to a gold earring post. It's really simple; the problem is finding suitable beads. The necklace and rings are weird; you could get away with taking a large large clear blue teardrop necklace pendant, gluing a red gem to the top of the loop where chains pass through, and wearing it on a gold chain. The rings are double-ended with small red cabochons in a spiral setting and two iron cross-shaped flowers on each side; I'd recommend either just using two matching red rings with round gems in a silver band, or finding a silver band and adding the decoration and gems yourself. (I'll be posting pictures of what the official necklace and official ring look like in the main HMC thread, for people who want to copy them.)
For the wig, I'd recommend the Bob from Cosplay.com
, in 24B, H24B/613, or H24B/613A depending on your skin tone and what type of blonde suits you. If you want to do a black-haired outfit, if your skin is darker or your hair is naturally dark, order 1 (true black), but if you're pale or hella blonde or something, 2 (espresso) is a better choice. (If you look in my gallery, you can see on the second page of my Howl pictures what it looks like when I wear that wig in a dark color for my Child Howl costume.)