For normal TV use (like you said) it would be great with the 4K screen and 43" as well.
For gaming, not so much. It probably has a low (real) refresh rate and 4K is hard to achieve unless you have 1080 or higher graphic card.
http://gpu.userbenchmark.com/Compare/Intel-HD-520-Mobile-Skylake-vs-AMD-Radeon-R5/m36797vsm12264
I can't really tell because the site doesn't have the exact model. But why do you want to know? Its not like you would switch between them.
Really depends on if you want more picture quality for a higher price. The 7th gen i5 vs the 6th isnt a big difference but can help slightly in video editing and such.
120GB SSD is a little small. I recommend at least a 240GB.
Some affordable 240GBs I recommend are: A-Data Premier SP550 240GB ($60), OCZ Trion 240GB ($62), or the more expensive but faster 850 EVO ($70).
Good luck and good day! :D