A size of about 100K (100000) is a reasonable choice.
Note: On windows in versions prior to 3.2.0 if the install location contains a space then you have to provide the shortname ( =c:\progra~1\Path\To\Install).
You can download it from here, place it into idp.home/edit-webapp/WEB-INF/lib/, then change to idp.home and run. The IdP status page at /idp/status is built with JSP and will not work without this library.
Monitoring Tomcat 8.0 with JMX prior to the full initialization of the IdP web application appears to destablize the Spring environment or trigger some kind of bug, as noted here.