I’m in the process of hardening and optimising a Windows 7 build at present. Did you know it has 150+ services now? Windows is officially big.
If you’re interested in this undertaking, I can recommend the Black Viper resource. There are a considerable number of services that can be disabled for most users. That said, you should not take the advice in this or other hardening links at face value. If the recommendations or documentation on the service is insufficient to make your decision, either leave it be or research it further (or both). This is the best opportunity you’ll get to fill any gaps in your knowledge.
Once you think you’ve got it licked, always test, pilot and refine an image. It’s also worth creating a log of your decisions for each service from the start, both as a knowledge base and for tracking changes and differences from default builds. The process of documenting your choice will force you to think it through and will give the question the gravity it deserves. There’s no question this is a laborious undertaking, but it’s a valuable exercise and should yield a build that you’ll be happy with for some time.