Setting the default shell to /bin/false means that su will switch user, and then execute
/bin/false -c /opt/tomcat/bin/startup.sh
You can use the -s option to su to override the setting in /etc/passwd, but this is only permitted if the calling user is root, or the existing entry in /etc/passwd is listed in /etc/shells.
Is this possible to have multiple address on single PC?
You can use the whole 127.0.0.0/8 network locally.
This means all addresses from 127.0.0.1 to 127.255.255.254 are at your disposal.
What is the best practice for running multiple server on same server?
With different IP address (127.0.0.1, 127.0.0.2)
With same IP address but different port (127.0.0.1:...