Well you see, your i7 4700 CPU costs $309 although it's barely faster than am i5 4570 which only costs $200. You paid 50% more for like 5% more performance. And especially in games you won't notice any difference between them, because they're GPU bottlenecked for the most part. An i7 is only worth it, if you regularily use programs that benefit from Hyperthreading, the only feature that sets the i7 apart from the i5. With those additional $100, you could have bought a much better GPU.
About the SSD, you should really consider buying one. Running your OS of it means a world's difference. I would rather first get an SSD than additional RAM.
You're absolutely right about your PSU not needing to be a nuclear generator, 450W would be more than enough. However, with cheap I referred to the manufacturer of the PSU. Cheap PSUs by no-name brands are a literal danger to your hardware. If it fails, it's very likely to kill your hardware as well because cheap PSUs lack protection mechanisms.
