Good info in #6. It might also be worth knowing that buying the higher resolution version will readily downscale to a lower resolution output (screen) and look as good as it can look at lower resolutions. However, that doesn't work the other way: buy (or shoot) low resolution and then try to play back on a higher resolution screen and it will look poor on a better display.
In pursuit of quality, best option is to always buy (or shoot) at highest possible resolution and watch it at lower resolution if that is the screen that is available. Especially when shooting video, you don't get to come back to now from the future to re-capture some precious video at a better resolution when you have a 4K TV... or an 8K TV or a 16K TV. Watch any video shot in VHS from a few decades on a modern set and you'll get this immediately.
And OP, if you give that particular movie a relatively little while, you can probably pick up the USED disc on Amazon, Ebay or similar for LESS than what a digital version costs. Learn to rip it yourself to enjoy it in all of the ways you can enjoy the digital version purchase, including several beyond what is possible with the digital version. You'll save money and can optionally make your render have less compression and thus better picture & sound.