Headphones are never going to give you the presence that a good HT setup will, especially when it comes to things like bass and positioning that a good speaker/sub can provide.
If you are using it mainly for movies (especially blu ray or 4k) you are missing out on one of the main aspects of the film. Even older movies can sound amazing with a decent speaker system driving it and good audio mixing.
As far as "not" enough room, you don't need a massive room for a HT setup and there are multiple ways and speaker setups to accommodate almost any room size/shape, etc, from in-wall/ceiling, to bookshelves, to towers.
I went with bookshelves (to me a good bookshelf + sub is better then a floorstanding speaker).I went with the SVS ultra's for my 5 speakers and then 4 elac a4's for atmos (since I didn't want to drill into the ceiling). A few speaker stands and some blu tack (this is a lifesaver when it comes to speakers and stands) and have my HT setup in a fairly small room (14x13ft and 8 ft ceiling).
After moving from my old speakers I feel like every movie I watch I'm hearing something new in it or I missed out on so many great soundtracks in the past because I had been listening to it on either headphones are cheap speakers (I was using logitech z5500's for a long time, so no DTS HD or anything).
That's not even getting into one of the best "new" things when it comes to HT's, Dolby Atmos.
Watching movies like Mad Max Fury Road, Hacksaw Ridge, and John Wick? It's like an Eargasm throughout the whole movie.
If you can afford it and it's in your budget for building a HT with a new 4k tv I highly recommend a good speaker/atmos setup. You don't have to go crazy on it, a modest 7.2 capable receiver with atmos support and just 5 main speakers/2 atmos can be done without breaking the bank.
Getting into the 5.x.4 or 7.x.4 speakers is a bit expensive though, a good a/v receiver that can support that many speakers will set you back around 900 bucks (at least last I checked).
