After installing WordPress, I have Twenty Sixteen theme out of the box. I’d like to modify this Twenty Sixteen theme (change css and js files) to get my own design and then sell this new theme.
May I do this?
Or should I make my own html/css layout from the zero?
in my opinion better to go professional by using some frameworks that u can start on
check this http://underscores.me/
It’s been asked loads before and I am not 100% on the answer but either way you would be hard pushed to create something up to par here by just editing JS and CSS of a free theme let alone all the modifications you would have to make to meet submission requirements.
You are much better off with your own setup or one of the frameworks that exist
May I use modified Storefront for my aims?
Unlikely given that all products etc. WooThemes.com have licenses which expire and need to be renewed annually.