-mainboard
Yes, I was thinking about a z77 chipset too. That's the best you get right now for that price range and it works great with a i5. Anyone of the mainboards you were thinking about will do more than what you need of it right now, ensuring that you can evolve your pc in the future without needing to buy a whole new mainboard. Just look at the specs, try finding other mainboards and if you don't see any significant difference, take the cheaper one
-cpu
As for the CPU I was thinking of getting the "Intel Core i5 Ivy Bridge 3570K - 3.4 GHz - 6 MB L3 Cache - LGA 1155 Socket" but people kept telling me it sucks and the Xeon is better
People are stupid. I'd say get the i7, but since your price range is of about 1000e, there's nothing better than the i5 3570K. That's the best performance/price ratio you'll get. Completely forget about the xeon, it never existed. The core i5 3450 is also a nice choice if you go overbudget and need to cut into your parts

You really won't see much difference right now and the 3450 should be around 30e cheaper than the 3570K (I'm thinking ahead, as you'll need to have some money left to buy a TFT

)
-RAM
For the RAM as I said any kit of 8GB DDR3 (1600MHz) will do the job. The mainboards you have chosen can probably go up to 32 or more GB but there's no software out there that you'll use that will use that kind of memory. Just keep in mind that you probably only have 4 slots on the mainboard (look through the specs to be sure) so if you can get 2x4GB it's better than 4x2GB, again that way you can upgrade your baby later on with less cost. Don't get tempted to buy a 16GB, we need to keep the costs down.
-SSD
For the SSD anything around 32GB to 64GB is enough. You'll only put your OS and programs in there (fast, silent usage) and you'll use the HDD for your files like music and such. But it's really optional, you can also add that later on. Actually it will probably be hard to get one without going overbudget mh...
-GPU
I can't open the gpu link (probably linked to some session var that i obviously don't have). For the gpu nowadays most stuff will do the job. You should stay with the radeon right now. So if you want to keep some more money, a radeon 7850 is great perf/price-wise and any radeon above will do the job. But considering the prices as i remember them (it's been some time now lol) i'd either go with the radeon 7870 or the cheaper radeon 7850. You won't see any difference afaik in actual games (and future ones for some time still).
To sum up: Prices are an estimate at best, I haven't seen prices for months now. It's just about how i remember it. :
i5 3450 , 8GB RAM (or even a cheap 4GB) , radeon hd 7850 , 500GB or 1TB HDD , no ssd , a normal 20e dvd-drive , a case + supply for max 150-200e
= 800e pc with super great perf/price ratio and easily upgradable. Add keyboard, mouse and a nice TFT and you have a great 1000e pc.
Go for the more expensive i5 3570K , radeon 7870 , SSD and about 50e for a blueray drive
= 1000-1100e pc with super great perf/price, upgradable as always but you'll still have to buy a TFT and mouse + keyboard.
PS: As I said before, when you know which mainboard you want, the rest builds around it.
Your 3 basic parts are: 1155 socket, Core i5, radeon HD. The rest of the parts don't have compatibility conditions.
For example if you find an AM3 socket main that looks nice, you won't go for a i5 but a AM3 cpu like a phenom II.