I see you're worried about the "playing on a TV" part. Honestly, there is 0 difference for a PC to run a game on a TV or a gaming monitor - the only difference between these two is the input-lag, which means, a gaming monitor will have something like a 1ms inpug lag delay, and the TV will have ~10-25ms delay. That's really the only difference. Unless you're used to very fast paced shooters with 100+ frames per second at least, you should see no difference. I personally enjoy TV much more than a regular monitor, because TV has much brighter and better colors.
Now the technical side
+some additional info:
GTX1050Ti is that real mid range GPU.
GTX1060 is considered to be the upper mid range of GPUS.
Talking about maxed out settings on newest games: 1050Ti will get about 40-45fps average and a 1060 will get 55-60fps on average at 1080p resolution.
Now about a 1050Ti. Is it a no-no? No.
It depends on your decision. From what you've said, i understand there are 2 options:
1. Playing on a 4K resolution natively and seeing as many pixels as the TV can show you - i wouldn't go below a GTX1060 (i will explain a bit later).
2. Reducing in game resolution to 1080p (4 times lower). There will be no issues, because 1 pixel of 1080p is equal to 4 pixels of 4K. If you plan on playing with a controller while sitting on a couch, it's a very viable option. There isn't much of a difference in 1080p or 2160p while sitting at 5+ meters away from the screen. In this case i think even a GTX1050 (non-Ti) would suffice taking in consideration the game is 6 years old.
Also, another fun fact about Nvidia's GPUs. You might find this interesting: how Nvidia names their cards:
First number is the generation, second number is performance rating, "Ti" = improved version, but not as strong as the next in <performance number+1>. For example a GTX1050 is a 10th generation card with a strenght rating of 5 out of 8 (because there is no gtx1090).
You can also check "game-debate.com" for graphics cards - all GPUs are rated there in how they perform in a specific resolution. Here you can see (http://www.game-debate.com/hardware/index.php?gid=3669&graphics=GeForce%20GTX%201050%20Ti%204GB) a GTX1050Ti has a 1080p rating of 8.6 where 10 is maxed out settings at 60frames per second on latest AAA games. But it's 4k performance is rated only for 4.6/10. So that's why i recommended at least a GTX1060 if you decide to play at 4K. For comparison: (http://www.game-debate.com/hardware/index.php?gid=3540&graphics=GeForce%20GTX%201060) a GTX1060 has a 1080p rating 10/10 and 4K rating 5.9/10 for newest games. Add the age of the planetside 2 and the results should look promising at native 4K resolution of your TV.
In summary:
For playing at 4K natively - nothing less than a GTX1060.
For playing at 4K with in-game resolution reduced to 1080p (or resolution scale set from 100% to 50%, bacause 2160p * 50% = 1080p) - You should be fine with a GTX1050/1050Ti.
Damn, i wrote a whole article there, anyway, i hope i helped you out!