This would be great. Your current build is quite balanced , good choice for a low budget. Your current build is like 2 steps below entry level gaming PC.
So here are some good upgrades.
A better PSU would be good so that you can get future upgrades without changing the PSU. And furthermore, it's more efficient, so it draws less power from your wall socket but provides the same amount of power.
A Haswell competitor would be the i5-4570 or maybe the i5-4440
The i5-3450 is Intel's 3rd Gen Ivy Bridge CPU while the i5-4430 is the 4th Gen Haswell.
Since the i5-4430 Uses the newer socket, there could be possible future CPUs using the same socket, thus making the motherboard future-proof.
For the motherboard, the current Intel motherboard you currently have is very basic. Not much features, but it's good to go lower on it and get a better GPU but it's your choice.
Go a little higher on the PSU and GPU.
Now for the PSU. A lot of people in the past have been skimping on their PSU, getting a low quality one. That's a very bad choice. Worst case scenario , PC blows up XD
but that's unlikely
A good PSU should be efficient and long lasting. The Corsair CX500 fits the bill. It's not very good nor is it rubbish, but it's a good affordable one. That VIP PSU doesn't seem to have very good reviews and their quality doesn't seem very high.
Yes. All the motherboard needs to support the HD 7870 is a PCIe x16 slot, which you have. But remember, it's a dual slot card so it's bigger than your current one. You would also have to open another slot at the back of your case for the GPU.
So it would look something like this at the back of your case