You don't actually need to use the SDk in this case. When creating alerts (which are checked by default every minute), you can have one or more actions triggered. These could include sending gets/posts to a web service, or perhaps running a script. You can pass variables from the alerting object to the trigger action.
There are training videos on customizing alerts here: Network Performance Monitor (NPM) Training - SolarWinds Worldwide, LLC. Help and Support
One note of caution, 20k elements would be more than a server can handle at default polling intervals (assuming you are referring to NPM, since you refer to elements). If you haven't an additional polling engine deployed I would recommend contacting your account manager to discuss further.