why don't you first try your Sammy built-in movie function if its good in playing the movies rather using a media player... also try out some 4K movies there
for the upgrades, here's what I'd do if I were you. since you're 95% on movies and has a 4K TV, you may follow this upgrade steps:
-- Nvidia Sh -- as I see you have FHD media player already and 3TBs of HDD so I assume that you download and watch offline movies. NShield player would give you a better edge in playing both 1080p & 4K movies., even better on HDR mode. but you may drop this to lower priority if you see that your Sammy 4K TV plays good enough with 4K HDR movies. BTW, this Shield will also give you some GForceNow games, Android games and even old classic games via an Emulator. you have the best medial player on the planet + ability to play games with it.
-- Atmos/DTS:X-capable AVR not necessarily Onkyo -- since you're getting a shield and has 4K TV and collects movies to your HDD, then why not jump the bandwagon on Atmos/DTS:X, right?
-- slow down on the 4TB HDD, unless you're really running out of space
-- put the 1080p Projector on your last priority -- this may have the highest expense in your plan given the brand/PQ of the projector of your choosing+ the accessories expense for the screen/stands/roll-ups, etc...
-- and then the PS4, if you'd still like to play games more
