Generally there shouldnt be any problems slapping Cloudflare on top of your current configuration. SSL should also work fine, depending on your current settings though. However if you are satisfied with your site’s performance and Wordpress knows how to handle DoS attacks - given you are concerned with that - there wouldnt be real need to switch.
I thought that Wordpress would be fine for CDN and DoS.
I was considering Cloudflare as I have always used them with my self-hosted sites and when I moved to wordpress.com, Cloudflare automatically emailed me to say that I was not now going through them.
I really cant comment on Wordpress’ ability in distributed content delivery, respectively attack mitigation. If they provide a decent service in this context there is probably little need to additionally configure Cloudflare. If they dont (and these areas are of concern) you might still want to consider Cloudflare.