Here are my suggestions for sizing images for posting in Critique Corner:
Size your image to not larger than 1024 pixels in either direction (that's the guideline max.).
In Photoshop use Image->Image Size and enable Resampling (this will downsample your larger image to the new smaller size by throwing away some of the information, so save this smaller version under a different name from your original or you may lose your original).
Do not be confused by the dimensions in inches or the DPI value - those are irrelevant. The size of the image on a monitor depends only on the screen resolution of that monitor and the number of pixels in your image. For example, most monitors are set for screen resolution of 70 to 100 pixels per inch. That means that an 800 pixel image dimension will actually be from 8" to 11" on the monitor.
In order to stay under the 100kB limit on file size, use JPG compression quality low enough to get under 100 kB by watching the file size change as you adjust the quality slider. It may be a little in error, so stay under 90 kB to be safe.
If the file size limit poses problems, you may want to host on another site and place a link to the image hosted elsewhere, but the 1024 pixel maximum still applies.
A related issue is the EXIF data. In order to be sure that your EXIF data is available for the critique, do NOT use File->Save for Web. That process removes the EXIF data from the file. Following my suggestions above preserve the EXIF data in the file.