Good stuff! All potentially useful in a VTT. Your brushes could be clipped out into individual stamps and used to make campaign maps directly in VTTs.
I'm going to offer a slightly different VTT perspective from that of Tenia. Been using VTTs for both online and face-to-face gaming for 12 years or so and primarily with
MapTool.
Not all games use squares. Some use hex grids. Offering non-gridded versions is important to support those gamers. As was mentioned, all of the current VTT apps that I'm aware of can overlay grids on images so baked in grids are rarely necessary. A scale on the map in some out-of-the-way location is sufficient in most cases.
Most current VTTs can support maps of any grid resolution. So producing them at multiple resolutions isn't really needed. Maps are easily resized either outside the VTT app or inside. What helps is if your map is made at, for example, 100 pixels/grid then the resulting image is 800 x 1000 pixels for a map that is 8 x 10 grid squares. If someone wants to use it at 70 pixels the math is easy. Multiply by 8 x 70 and 10 x 70 and the new image is 560x700 pixels.
Don't diminish your art by using low quality JPEG settings. Save at a high setting and don't try to push for any specific MB file size. Yes, larger files take longer to transfer to clients but the difference between 1MB and 3MB isn't worth the quality loss.
More comments in general on making maps that are usable for VTTs can be find in my blog post here:
https://dqmusings.blogspot.com/2017/05/usable-maps.html
Thanks for sharing your work!