When you're assigning keywords to landing pages, this process should be dictated by the keywords you chose within Hike.
If you chose X keywords you want to SEO, then you need to make sure you have a sufficient number of pages to 'house' these.
What if you have left over pages of your website - should you add keywords to these?
Only if there are keywords that are relevant for these pages!
You don't have to add keywords to every page of your site, that's not needed for good SEO.
Hope this helps!