I planned and measured and planned and measured and planned... and still came -><- this close to buying the wrong screen size. Take your time. Strange factors can intervene - a big screen is also a tall screen, so how close to the ceiling is it? Will light fixtures be in the way of the projection (if the projector is ceiling mounted)? Have any tables between you and the screen? Footstools? Did you account for the screen border? How are you mounting the screen? Once mounted, how will you adjust it's height (or the projector's)? Do you have enough room on the sides for the speakers so they won't block the view of the screen, be too close to the side walls, be too close to the rear wall the screen is presumable mounted on (e.g., if rear ported - the classic "YouTube home theater problem" of fine speakers smack in the corner of the room because of the screen and room sizes), be too far out into the room, etc. Where will the center channel live? Have a stand of the right height? How will you angle it? Given the size of the screen will you be comfortable with your seating position? (i.e., close enough to "benefit from 4k" and not so close you're craning your neck or otherwise uncomfortable) Can your projector sit where it needs to be and project the exact size you need? (I like tools like the one at Projector Central for testing that stuff.)
More rabbit hole details - Projectors lose light output the "smaller" it makes the image at a given distance (i.e., the farther it throws it), so ideally it would be at one exact point - as wide open as possible and as close to the screen as possible - for max light output. How many lumens are you losing with your planned configuration, and does that still work for your screen size and room? If you have complete light control of the room, that's less likely to be an issue, but still worth thinking about - and if you have to deal with ambient lighting, you really need to think about it.
Finally, what adjustments does the projector have? (and the mount) Some need to sit with the center of the lens at a specific point - say, precisely in the center side-to-side, and exactly 1" above (or below, if on a table) the top edge of the screen. No adjustments. Does this work for you or present problems? Many have decent range flexibility, but short throw ones can limit you to 1 foot of placement flexibility for a particular screen size. (Measurements are typically from the front of the projector, so you don't have your full room depth.) Projectors with more adjustments built into them are more flexible (and expensive), but keep in mind than even then, their figures like "50% lens shift up/down and left/right" does NOT mean it can be 50% off up/down AND left/right - the more up (or down) it is, the less left (or right) it can go, and vice versa.
I don't suggest you answer all these questions here, of course, but since I literally ran into each and every one of these issues (and more), during my planning and implementation and had to make a variety of changes based on my answers, I wanted to raise them for you. It's a complete pain to end up ordering a big screen and low-lumen projector that just barely works, only to realize you have to mount it at the back of it's range and you lose 30% of your light, leaving you feeling like everything is too dim. (Fortunately, I did NOT experience that one. Although I was annoyed at how much output my lamp lost when I got near lamp expiration.)
For 1080p the BenQ series projectors are inexpensive and well regarded. I used to run a HT2150ST because I wanted the short throw and low input lag for gaming, and when adjusted with "settings you can find on the internet" and a test disc, I really enjoyed the image through the lifetime of two bulbs. Their other similar projectors are also well regarded. The HT3550 is definitely a step up.
While I didn't spend time with the Epson 5040, I bought the 5050 and have been very happy with it and it's a big upgrade over the BenQ, and "4k/faux k." Unless the 5040 is on a really good sale or something, I'd suggest the 5050 as much better, based on the reading I did at the time - but I confess I did not directly compare in person.
So those are my suggestions for the sub-$1,000 and ~$3,000 price point. Everyone swears by JVC in the $5,000+ zone, but I wasn't going there. Sorry I don't have a better answer for ~$1,500-$2,000, but when I was researching ~6 months ago, I would have probably gone with the HT3550. BTW, you really need a bit of a light canon for HDR. My screen is 142" for 2.35:1 and 114" for 16:9 (the Epson's lens memory is wonderful for this, if you care about 2.35) and the Epson is near minimum distance, and I consider it barely bright enough to do HDR in a fully light controlled room at the 2.35:1 size.
