So in general for level 3 and 4 DDoS attacks we absorb those silently at our edge. Customers never even know about them because we never send any of the resulting traffic to the origin servers. Cloudflare doesn’t currently have an alert system on any pan level for DDoS mitigation. We are working on additional tooling for more automated advanced DDoS mitigation and detection for our higher tier plans and some notification mechanism for customers is under consideration.
Website defacement monitoring isn’t a service Cloudflare provides. We do provide a Web Application Firewall which is intended to protect a website against malicious attacks which could result in such defacement.
DNSSEC is available at any plan level (including free).