I would wait if you can for a 4k tv. ATSC 3.0 will come out in 2020 sometime. I would personally want the ability to watch TV in 4k over an antenna. It's the least compressed version of a tv signal and with cord cutting, broadcast tv is just going to get better. The major networks have already announce some plans to add channels. I already get 50 or so channels over my antenna, ATSC 3.0 will give the stations the capacity to add more.
There is only a handful of places you can get 4k content right now. It's far from a necessity at this point. ATSC 3.0 should change that. The built in tuners are always better than the boxes that you can add on.