JBoss AS uses an embedded copy of JBoss Web, which is based on Tomcat, to handle HTTP requests. Thus the request thread configuration options for JBoss AS as the same as for Tomcat and are configured in the server/xxx/deploy/jbossweb.sar/server.xml file.
The issues you had with more than 1000 threads is probably not Tomcat-related. I suspect that either your OS or hardware was chocking with so many threads running. Or it could be a JVM heap issue. But without gathering performance data to analyze the problem, it is hard to say.