I checked the file size of 7 or 8 member's avatars, and the largest among those is 27 KB. So, if you can shrink yours down so that it is 27 KB or smaller, you should be
fine.
In addition, all of them were jpg format except one, which was gif. I don't recommend gif, as it isn't intended for highly detailed images with subtle color variations, and probably won't look as
good, unless your avatar is a cartoon image or something similar.
Hope this helps.
-BH