Mixing WP with an existing site

I already have an existing PHP site which doesn’t have any particular framework behind other than custom code to perform some basic content management. It seems to me that WP would be ideal to take on the role of displaying content however I wanted to make sure that WP could handle both the WP content display with my own requirements for the UI, existing pages which serve dynamic content, etc.

So for example the front page would have the news and some sticky content all sourced from WP with nav links to other WP pages and also other non-WP locations. I am almost sure this is fine but wanted to check with the group for best practices, gotchas, etc.