How and what is your room dimensions first? It's critical to determine what kinda setup you should go for.

Example if you do not have adequate space behind your seating position, there's no point doing 7.1.2 if the surround back speakers are going to be 6 inches from the back of your head. It would be better to do 5.1.4 instead in that case.

"Brand and model" is a vague term. Too vague to give an answer to. What are you talking about in those terms? Speakers or receiver?

16x20 is not a rectangle, you'll be dealing with a lot of irregular room modes and 2nd order cancelations.

Screen size is up to your decision if you're placing the speakers behind an acoustically transparent screen or not. If you aren't, then of course you'll have to lower the screen size to accommodate placing the L and R mains.

If you're following the 1/3rd couch placement rule, then you shouldn't have an issue placing the surround back channels to make up the bed layer 7.1 channels. To be frank with you, if you're only going to do 2 height channels then I suggest not to do it at all. It's kinda pointless at that point especially when Dolby Atmos track mixes for home audio is already pretty bad to begin with. I don't see why you can't go for the full 7.1.4 setup though, it'll fit fine in the room if you ask me.

Side note: there is no .2 in the channel designation of a speaker layout (i.e 7.x.2/4/6). The sub channel is ALWAYS a mono signal, not stereo. You can have a hundred subs in the room, it's still only a .1 channel.

Does your budget includes BOTH speakers and AVR (what about room treatments?)? Because if so, it might not actually be enough at max RM30k.

It's a common misconception I think when people mention the number of subs in a channel setup. Because when someone has 2 subs, I guess it's in some way proper to say they have 5.2.2 setup for example. They use the number as how many speakers they have in the system, except that number isn't used for the quantity of speakers, it's actual definition is the number of channels.

Channels =/= to quantity of speakers. When you go to a commercial cinema, you'll see they have like 5 main speakers behind the screen, 18 surround speakers, 20 over heads and 10 surround back speakers and 4 subs for example. But despite that, do you see a THX certified cinema call it a 33.4.20 channel setup? They of course don't because the signal is still just a 7.1.36 (36 being the heights for Atmos). Similarly I have 6 subs in my room, it doesn't mean I call my system 7.6.4 ya know? 

I don't have enough experience with projectors in general though, so I'm not the best person to ask regarding projectors. I do know that Optoma UHD35+ is a pretty decent projector however.

There are acoustically transparent screens you can use if you want to put speakers behind it. For movies, it is the best setup because you don't have to compromise on the center channel (which is by far the most important speaker in a multi-channel setup) with a typical horizontal MTM design speaker. You could use vertical (which is the best way how woofers and tweeters should be aligned) MTM bookshelves behind a screen for no issues with lobing or phase shifts when listening off-axis.

i worry the screen will obstruct the speaker sound going through.
https://www.xyscreen.com/acoustic-screen-ma...reen-xy-screens
look for acoustic transparent screen.

How was the result ?