I cannot comment in detail, but here are the basics, rearranged for recommended order of installation:
2. PostgreSQL and Mysql are standard Ubuntu packages and can be downloaded and installed using apt-get, synaptic, or one of the other Ubuntu/Debian package tools. Some post-installation configuration may be required, and the best place to get details is on a Ubuntu forum or how-to web page, for which you'll probably have to do a web search.
1. Tomcat may be available as a Ubuntu package, but I generally just download the Tomcat ZIP file from tomcat.apache.org and unzip it. For development, I usually just unzip it into my home directory.
3. Likewise, download Eclipse and unzip from Eclipse.org - you'll want the J2EE bundle, which is fairly large. I also typically unzip Eclipse into my home directory. For convenience I like to define a desktop/menu shortcut to /home/me/eclipse/eclipse (where "me" is my userId).
4. It's a good idea to edit your profile to add the following 2 lines:
Your Java may be installed somewhere other than /usr/java (default is a softlink to the preferred JDK directory). Adjust accordingly. You should NOT attempt to use the freebie Java that comes with Linux! It's still not powerful enough for this kind of stuff, so download and install a Sun/Oracle JDK!
An IDE is no substitute for an Intelligent Developer.