To give another deviant a direct link to this FAQ answer, use the following code in your comment or forum post:
How many avatars am I allowed to post in one comment or journal?
There is no actual limit, but administration states that deviants only display sixty four avatars. That is eight rows of eight. More than plenty to display your friends.
Note that as subscriber, you have the option to show the avatars of your friends automatically below your journal.
