How to show sub-categories and reduce the number of required information for create_account.php?

[after8hrs]

Q1: How to show sub-categories of products on index.php?

 

I want to show at least the next-level product category on the homepage, even better if the next next level sub-categories can show on homepage. How can I achieve this, please?

 

Q2: How to reduce the number of required information for create_account.php?

 

I hope to make 2 more items not required, they are street address and post code.

[after8hrs]

I will have to add one more question:

Q3: Which file should I modify so as to get rid of the Welcome Guest! Would you like to log yourself in? Or would you prefer to create an account? but still keep the other greeting words on top of these(in red color)?