I believe only Samsung, LG, AUO, and Sharp manufacture TV panels today. All other brands buy the panel from one of these companies, and adds their own electronics and cases. Yes this means Sony doesn't make their panels. As of a few years ago, Sony TVs typically used a Samsung panel (they partnered with Samsung in developing panel manufacturing, but sold their share to Samsung in 2011). But I don't if that's still the case. That said, it's generally acknowledged that Sony has very good image processing electronics which, to the discriminating viewer, can produce a (slightly) superior image even on a the same panel.
As long as you stick to the big brands, you should be safe. You may want to visit a big box store and compare the user interface and menu options side by side. I find those make a big difference in how you'll use the TV (particularly, channel selection, favorites, etc - maybe not if you'll always be using a cable box). Ignore the picture quality unless the store lets you tweak it. Usually the image settings on display TVs are too bright, oversaturated, and oversharpened, making them pretty useless for a side-by-side comparison.
The larger the TV the easier it will be to see the pixels on a 1080p screen, and the more useful 4k can be. For anything below about 50", I wouldn't bother with 4k. At that size you have to be sitting like 6 feet from the TV to see the difference between 1080p and 4k. 50-69" is kinda borderline for 4k. 70+" I would definitely consider 4k. I use a 1080p projector to project a 130" image, and the pixels are totally obvious and distracting. I cannot wait to replace it with a 4k projector as soon as those become reasonable in price.