A token discovery!

[Dark_Soul]

I feel your pain. I got the Devin Night token bundle addon for my kickstarter pledge; it's something like 105 of his token packs.

[StoryWeaver]

I've always found 100x100 to be to small, makes the tokens unclear and blurry when you look at them. Particularly if you zoom into the map a little.
So I tend to used 256x256, similar to what roll20 uses for medium tokens.

[ColinBuckler]

You can use XnConvert to resize or transform multiple images at the same time. In otherwords drag all files image from a single folder and drop then into XnConvert and you can set a ru;e up to resize all images to 100x100px. Saves open each file up, resizing and then saving one by one.

Best thing about XnConvert is that its free!

https://www.xnview.com/en/xnconvert/