I actually did already sharpie them using a sharpie pro, which has yellow rubber grips on the side of it. I use that to stencil tennis racquet strings and it is more durable than regular sharpie. It looks good with the solid black grommets.
For the thumb loop, i went to the local leather shop and asked them what they had for scrap leather, which is too small for them to use for any projects. They let me dig through it all and i came up with a few pieces to try. I cut out the old broken part of the thumb loop and traced it on the new piece for a template. I then cut it to the right length, I also sanded down the under side edge, where your thumb slides over it. That made it a little more flush to the lining on the glove. Then, I sewed the new thumb loop in the same place as the old. To sew it through the leather, i used vise grips to push the needle with a doubled over thick white thread. Then i used a leather punch for the lacing (palm lacing) holes to also hold it down, just like the original. Here are some pictures below.