How to remove projects from the Recent Projects list in the Start Page?

/Users/<username>/Library/Application Support/NetBeans/<netbeans-version>/config/Preferences/org/netbeans/modules‌​/projectui.propertie‌​s

How can I set the JDK NetBeans runs on?

Update the netbeans.conf. You may need administrator privileges to edit the file.

/Applications/Apache NetBeans.app/Contents/Resources/netbeans/etc/netbeans.conf

and change the following line to point it where your Java installation is:

netbeans_jdkhome="/usr/local/opt/openjdk/libexec/openjdk.jdk/Contents/Home"