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#11
Windows doesn't need any third party programs/services to start up. However, some programs which depend on the services disabled may disfunction. They will start working when the appropriate service/s are enabled once again. However, disabling everything (except AV services and programs - ESET in your case) is crucial to efficiently testing a clean startup.
I don't understand the priority bit, priority of ESET? I don't think you would need to change its default.