Depending on workload, you may not need to do anything at all. Tomcat's out-of-the-box configuration is pretty serviceable. The main things I have to tailor tend to be stuff like copying in the database drivers that I need to the TOMCAT_HOME/lib directory.
The only real way to tell is to set up stress
testing that models what you're actually going to deploy and how people will be using it.
And yes, the disk drive that Tomcat's temp directory is located on should have a decent amount of free space, but usually that's not a lot of space required - unless a lot of people upload large files at the same time.
The secret of how to be miserable is to constantly expect things are going to happen the way that they are "supposed" to happen.
You can have faith, which carries the understanding that you may be disappointed. Then there's being a willfully-blind idiot, which virtually guarantees it.