I would prioritise getting the correct size TV with the best possible picture for your budget. 4k enabled obviously, but remember we don't all watch TV a lot of the time in 4k so the standard and HD picture needs to be good.
Android TV boxes (I won't bang on again about them) are capable of playing 3d movies and there is some (free) content available. But like Markymark said, it is a failing format that never really took off (a bit like Mini discs).
I really enjoyed the 3D experiences at Universal Studios but looking back that was only because I was in a roller-coaster type simulation. We saw a Minions one in normal 3D on a static seat and it was really boring and blurry in comparison.
The quality and resolution of the picture, in my mind, is still the most important feature. If you're watching in 4k then you have the luxury of buying a larger screen that (at the same viewing distance) would otherwise look grainy in SD or even 1080p.