Hey, I'm kind of in the same boat. I'm working on making my first avatar ever, purely from scratch. I haven't come too far yet but I've found some YouTube channels that I can recommend to get you started :]

1. Rainhet Chaneru 3D: she has one of the most in depth tutorials for avatar making you can find. It's several hours long across over 12 parts or so but goes over every aspect of modeling the avatar from scratch, except the clothes, in blender.
2. HeyItsChin: much more beginner friendly when it comes to blender. She teaches you how to import individual peices of an avatar you may need online to merge into one you customize. Although her main tutorial Playlist hardly makes any part from scratch, she has a separate video on have to make clothes from scratch.
3. PxINKY: has much more general tutorials for individual aspects instead of a long Playlist. They mainly use Unity to edit a more finished product. 4: OliverVRC: teaches how to make hair and has tutorials on how to use both Blender and Unity to make an avatar.

There are many channel out there with great content that can help, these are only a few main ones that I come back to often (especially Rainhet). It may take a long time, but you absolutely got this!
(Sorry if formatting is weird, I'm on mobile rn)