Splunk documentation (which @richgalloway already pointed you to) lists minimal recommended values.
As with any resource-related question, without a precisely formulated requirements and circumstances there is no one good answer and usually "the more, the better".
You have to ask yourself what are the ulimits and what purpose they serve. They are limits that system enforces on a particular user and they are in place not to help a single process or user but rather to prevent one user from "overrunning" whole server and starving it out of resources. Therefore ulimits are usually set relatively low on servers with many concurrent users (like old-style unix servers in university departments on which many users work at the same time), they might have some use on your local laptop where you might have different services working with different user's accounts but don't make much sense in a single-purpose single-service server.
