best way to format subcategories for directory site

I'm building a fairly simple directory site. I have a category page set up, on it is a table with subcategories that are linked to their respective page. All of the subcategories are in a list tag. I'm not sure the best way to format it now though.

First question:

Should I use a heading tag for the subcategories? Right now the page title is <h1> and some text saying "Please choose from the list below" is my <h2>. Not sure if I should use <h3> tag or just regular text.

Second question (SEO related):

Will having the list of subcategories look like keyword stuffing to google? Lets say my page title is "Marketing." If I have a bunch of subcategories with various types of marketing there will be a shit ton of keyword on the page. Will something like this hurt the site? And is there a good way to fix the issue?

Thanks

afternoon bump

People say h1 is important but I never use them. Just don't stuff.