What is the rest of the room like and what is the intended use? Is the room only for TV/Movies or is it a general gathering place in the house like a family room/rec room? What is the lighting? Are acoustic treatments an option? 2-channel music as well or just video sources? Room size/shape? Hard reflective surfaces like concrete, hardwood flooring, and windows? Which model Thiel speakers?
In my experience, a projector and separate screen is great for a dedicated home theatre, but in a mixed use room that will have significantly more ambient light, you might be better off with a large LED/OLED/etc TV. Aside from the cost savings, you don't have to worry as much about the ambient light, line-of-sight, installing and running cables through your ceiling (I know ultra-short throw projectors exist, but are more expensive for a given picture quality and still best in dark rooms). Plus if you ever move, it's easier to take a TV with you to repurpose elsewhere if the new place doesn't have the option for a dedicated theatre space.
A huge screen may help to make you feel a part of the action, but the room has to be large enough for you to actually take it all in, and not all spaces are...its why the front row of a movie theatre isn't typically the best seat. Depending on the room size and seating distance, 75" might be plenty and splurging for a 120"-200" projection system might not necessarily make it more enjoyable...as sacrilegious as that feels to say. If your room is big enough, I'm all for having an IMAX screen in your house.
As another post noted, I think you may have the lingo a bit confused and that could cause further confusion down the road. a 2.1 system means 2 front stereo speakers (front left & front right) plus 1 subwoofer. This would not include a center channel speaker at all. Somewhere in the settings of your system you would configure the sound to output in strictly stereo and anything that would have otherwise gone to the center channel in a full surround setup would instead come from the two front speakers (except low frequency stuff sent instead to the subwoofer). This is sometimes referred to as having a "ghost" or "phantom" center channel if you include surround channels but no center channel. A 3.1 setup would be 3 front speakers (right, left, & center) plus a subwoofer...in this setup it is important that the 3 front speakers match as closely as possible or else you'd be better off with 2.1 instead and running in stereo. A 5.1 system would include a center and surround channels...most feel that the surround channels matching is far less important than the front 3 matching. So the first number is the number of speakers around on the same flat plane as you and the screen...the number after the first "." is the number of subwoofers...if there is a second "." and another number, that would indicate "height" speakers; such as those installed in the ceiling to make noise seem to come from above you.
Since this seems to be intended for movies/TV then I think a good subwoofer is an absolute must have, and even better with multiple subs if the room/budget will allow. Some would argue, but I personally think even mediocre surround channels make watching far more enveloping. It's easy to make good stereo speakers create a phantom center, but the only way to make it sound like something is coming up behind you in a suspenseful scene is for a speaker to be behind you playing that sound. If your room allows for surround speakers, I'd spend money on the 75" TV, a Home Theatre Receiver with pre-outs and room correction, a good amp to drive those Thiel speakers (connected via said pre-outs and set up for a phantom center so you don't have to worry about matching), a solid subwoofer, and get a pair of budget friendly surround speakers the receiver can drive so you get that true surround experience...but that's just me.
In my experience, a projector and separate screen is great for a dedicated home theatre, but in a mixed use room that will have significantly more ambient light, you might be better off with a large LED/OLED/etc TV. Aside from the cost savings, you don't have to worry as much about the ambient light, line-of-sight, installing and running cables through your ceiling (I know ultra-short throw projectors exist, but are more expensive for a given picture quality and still best in dark rooms). Plus if you ever move, it's easier to take a TV with you to repurpose elsewhere if the new place doesn't have the option for a dedicated theatre space.
A huge screen may help to make you feel a part of the action, but the room has to be large enough for you to actually take it all in, and not all spaces are...its why the front row of a movie theatre isn't typically the best seat. Depending on the room size and seating distance, 75" might be plenty and splurging for a 120"-200" projection system might not necessarily make it more enjoyable...as sacrilegious as that feels to say. If your room is big enough, I'm all for having an IMAX screen in your house.
As another post noted, I think you may have the lingo a bit confused and that could cause further confusion down the road. a 2.1 system means 2 front stereo speakers (front left & front right) plus 1 subwoofer. This would not include a center channel speaker at all. Somewhere in the settings of your system you would configure the sound to output in strictly stereo and anything that would have otherwise gone to the center channel in a full surround setup would instead come from the two front speakers (except low frequency stuff sent instead to the subwoofer). This is sometimes referred to as having a "ghost" or "phantom" center channel if you include surround channels but no center channel. A 3.1 setup would be 3 front speakers (right, left, & center) plus a subwoofer...in this setup it is important that the 3 front speakers match as closely as possible or else you'd be better off with 2.1 instead and running in stereo. A 5.1 system would include a center and surround channels...most feel that the surround channels matching is far less important than the front 3 matching. So the first number is the number of speakers around on the same flat plane as you and the screen...the number after the first "." is the number of subwoofers...if there is a second "." and another number, that would indicate "height" speakers; such as those installed in the ceiling to make noise seem to come from above you.
Since this seems to be intended for movies/TV then I think a good subwoofer is an absolute must have, and even better with multiple subs if the room/budget will allow. Some would argue, but I personally think even mediocre surround channels make watching far more enveloping. It's easy to make good stereo speakers create a phantom center, but the only way to make it sound like something is coming up behind you in a suspenseful scene is for a speaker to be behind you playing that sound. If your room allows for surround speakers, I'd spend money on the 75" TV, a Home Theatre Receiver with pre-outs and room correction, a good amp to drive those Thiel speakers (connected via said pre-outs and set up for a phantom center so you don't have to worry about matching), a solid subwoofer, and get a pair of budget friendly surround speakers the receiver can drive so you get that true surround experience...but that's just me.