The raw assets (such as .PSD and .AI) are stored separately in Google Drive to keep the repo compact.
Turn the PNG art into pure black on transparent, such as using the Photoshop magic wand with 20 tolerance, anti - aliased. Then, use curves to force all set pixels to be black.
Use a tool like pngtosvg.com to convert it, with one color, to SVG.
Open it in Adobe Illustrator to adjust the viewbox as appropriate.
Voila! Make sure to optimize the resulting files as outlined below.
Images should be resized such that the longest dimension is <= 2000 px.
Generally save around quality 11 out of 12 for printed assets, 10 out of 12 for digital assets.
Use something like https://compresspng.com, which can generally achieve a 50% compression and supports bulk processing.
Precision can generally set be pretty low (ie 2 / 10) unless it makes it look terrible.
IMPORTANT: Make sure to preserve the viewBox setting.