Sorry, but now you have me confused.
The only network I have is my personal Apple network that is my AirPort Extreme
OK, got it. The AirPort Extreme is providing your wireless network at this time.
As mentioned the Airport Express IS the only network I have
It was mentioned in the first statement above that your AirPort Extreme provides your network at the present time. Do you also have an AirPort Express that might be "extending" the network that the AirPort Extreme is providing?
It was a good price,brand new in the box and thought it would replace the AirPort Extreme without any issues...
The TC can replace your AirPort Extreme if you set it up to run your network as you have the AirPort Extreme. I cannot say whether setting up the TC from scratch will be an "issue" for you, but it should not be since you already know how to set up an AirPort Extreme from scratch.
Since a TC is an AirPort Extreme (with a built-in hard drive), the setup of the TC would be the same that you used previously with the AirPort Extreme.
If you want the performance of the AirPort Extreme with hard drive storage capacity that the Time Capsule offers....with no additional space being consumed....then it would make sense to set up the Time Capsule as your router and storage device.
The downside.....If the TC goes down or has a problem, then you lose both your network router and the hard drive.