The perfect way is to visit a jewelry store. You can ask to measure your finger there and it's free. Or try rings there and look for the size, that matches the best.
If you can't, wrap a floss or a string around the base of your finger, marking where the first overlaps with a pen. Then, line that up with a ruler and take down its length in millimeters. Search "Ring size chart" and find out your US size!

Yes and you'll get them printed with your order!

Yes!

If you like a ring, but you need it to be made adjustable, just write me down!

Other changes or ideas are fine as well, do not hesitate to contact me :)

Only the top layer of metal has turned the blackened color. Over time, even with the best of care, the oxidized finish will polish off and the true color of the silver will shine through. Don't worry, it'll still look beautiful and will develop a character unique to your wearing story.
If you'd like to get it oxidized again, I offer free re-oxidations. If you send your pieces back to me, I will re-oxidize and return them to you (I just ask that you pay for shipping).