Customizing your team does require credits - that is a premium feature - but that is just dealing with your team name, city, colors, etc. You should be able to do all of the other tasks involved with managing your team, purchasing credits gives you some premium features but gives you no competitive advantage.
As Punisher said, to hire coaches or sign players just perform a search and then offer them a contract. Once you've poked around a little bit you should get a feel for the flow. If you have any questions about how to do anything, just ask - there are lots of helpful folks in the community. But don't worry, there is no requirement to purchase credits to be able to do what you need to do.