Avatars and displaying character generators?

[GeneticAlpha]

I have a couple of questions. First is, I'm wondering how I can go about making it where users on my site automatically get a default avatar until they go to their profile settings. Their profile settings I'm wanting it to have like a small gallery to pick from. Essentially, not giving them the option of using their own avatars on the site but the MyBB forums they can. I tried using CSS to just hide the field text area of what's already on the registration page that would of worked on setting the default avatar, but for some reason every time I hid the field in different ways it decided to just not work lol.

Second question is, how would I go about putting on the user's public profile an image that is their generated character? and a generated character thing in their settings that they can edit that changes their public profile image?

I'm really wanting my user's to be able to customize their horse character and have a health system and fatigue but no php knowledge >_<...and looked through forums but can't find much on it.

Thanks!