If you want to upgrade or implement you need not to implement any kind of support package stack level that is based up on your source system, it will be comparatively greater in comparison to relative support package stack level of the release you are working on. Please make sure that the corresponding SPs or SP stack of the application as well as for the Net weaver release will be available while upgrading or applying any kind of support packages or at the time of implementing an enrichment package.
It is not so essential and even not suggested to implement the recent SP stack in your source system earlier doing an up gradation or to implementing EHP. Please ensure yourself to examine the alterations on a regular interval of time. Please be prepared to install new developed support packages regularly to remove problems which have been already corrected from arising in your SAP solution.
At the beginning time, you must be cleared about all the components that are being used in your system landscape. There can be known side effects for all the support packages that will be generated in case of your SP queue. You must have to use the latest version of the support packager manager earlier you applied any kind of another support packages. You ought to use 1 2004 SR1 in an ERP 2004 environment as soon as there will be availability and deployment of ERP 2004 SP Stack.
Hope this article might help you to understand the above issues.