Hello,
If you don't see the field in the seller info but see it on edit profile and registration page i think you have to check Detail page for the field in the Admin panel> Account fields> edit page
Automatic upload images setting is different thing and it's only for listing photos uploading not for other images.
Your second question is possible to do, you have to do few changes to the code:
1. includes/controllers/account_type.tpl
add new tab
Code:
Only registered members can view the code.
2. add phrase through Admin Panel>>Languages with key additional_details_tab and value you want to be name of the tab
3. templates/your_template/controllers/account_type.tpl 2 changes:
-1st change : remove or comment following code
Code:
Only registered members can view the code.
2nd : create new tab
Code:
Only registered members can view the code.