For most of this: "it depends"
It'll be easier to answer questions if you ask them individually, but it's unclear if and what documentation you've already read. Cluster setup is well documented. As you ask about "more performance": More than what? Databases are all good for production (apart from hsql). Check David's blog article "What Liferay won't say" (linked from the
latest Radio Liferay episode).
Liferay also offers consulting around the product, where a lot more details of the best practices are covered - this is possible for your architecture, infrastructure, go-live, tuning or other aspects of setting up a great system.
No matter if you install the tomcat bundle or separately, maintenance of tomcat is in your own hands and typically excluded from the Enterprise support - unless specifically booked. But they're not really different: You can just check a diff between the tomcat bundle and a vanilla download of the same version of Tomcat.
