Ja, englisch wäre der bessere Weg. Als “Anfänger” empfehle ich Dir dieses Buch über die Administration von Openfire.
Yeah, english would be the better way to go. Since openfire is based an java it consumes a lot of ram. Depending on the number of active users you should increase the java heap size.
This seems to be a JVM implementation issue - it seems to map java threads to unix processes. Actually there should be only one process with 50-100 threads.
As Openfire is based on Java it needs memory. Do you have only 380 MB physical memory?