1. I don't think there's a problem with older versions of maven, I recommend you just give it a try, you only need to change the maven version in prerequisites in the parent pom to your version and try the build. If it works, let me know and I'll lower the required maven version.
2. There is no problem with that, although this is currently not supported out-of-the-box in the installer for example. You would simply need to replace how it is currently configured for JBossAS with the tomcat equivalent. To get you started, this is what you should do. If anyone wants to improve the installer script to support tomcat as well, I would gladly accept the help ;)
If you run the installer for JBossAS, it generates and copies various artefacts. You can get those to work on tomcat by doing:
copy the jbpm-gwt-console.war and jbpm-gwt-console-server.war to TOMCAT_HOME/webapps
rename jbpm-gwt-console.war to jbpm-console.war (so it shows up on http://localhost:8080/jbpm-console
rename jbpm-gwt-console.war to gwt-console-server.war (so it shows up on http://localhost:8080/gwt-console-server
update TOMCAT_HOME/conf/tomcat-users.xml to include your users + roles
copy JBOSS_HOME/server/default/data/birt to TOMCAT_HOME/birt
copy h2.jar to TOMCAT_HOME/lib
update catalina.bat to set classpath variable jbpm.console.directory to the evaluation resources dir (unless you use guvnor as process repository)
copy all necessary dependencies that are not in the default tomcat classpath to TOMCAT_HOME/lib (or in the WEB-INF/lib folder of the gwt server war)
Kris