So, that's up to you, but here's my thoughts on that.
The Tyrfing will work, and for the record, only in specific situations does anybody look to full tower cases these days especially for gaming systems, but it doesn't have the greatest design for airflow as the front panel is restricted in such a way that it's pretty limited. You could do a lot worse though, so it will work. If you're willing to spend fifty bucks on a case, take a look at the Fractal design Focus G, which is a very good example of what a budget mid tower case SHOULD be.
The power supply, isn't very good, especially if it is more than two or three years old, but even if it isn't. Those EVGA B1, W1 and N1 units just don't usually tend to last very long when used with any graphics card that requires more than slot power, and often, not even with those. The fact that you've been using it for a while, assuming without problems, doesn't change that. It just means you've been lucky. These units, much like the older Corsair CX units, have a history of also occasionally taking something else out with them when they go, like motherboards.
If you're going to buy new hardware, do yourself a favor and protect that investment by also replacing the power supply and it would be wise to replace it with something that is substantially better quality than that one is. The capacity is fine, most systems need only a 650w or lower capacity unit for most graphics card models these days, but capacity doesn't mean much or even anything unless the build quality, protections and components used are known to be good as well.
What resolution are you (And planning to be) gaming at? Any plans for that to change anytime soon? Are you wishing to replace the graphics card too or planning to stick with the card you have and just change the platform?