@Goldmember, what @Yonnee says is right on the money regarding screen/room size. Too big a screen in a smallish room & all viewers will see pixelation, which is sorta like watching a movie through fishnet stockings.
Bear in mind that if you bought a theatre ticket, would you sit in the front row? My guess would be, not by choice, which again @Yonnee has it right. it's tiring if you have to move the head side to side & you miss so much.
The good news is that a smaller room will save you money across the board. You'll get away with a smaller amp, screen, air con, sound proofing & less carpet cleaning after film night.
In this day & age, a 46cm flat screen TV screen is very affordable, & plenty big enough for a bedroom makeover. I love the idea of retractable screens & projectors, but in a dedicated theatre room, what's the point?
Be discerning about your sound system, too bassy, & the critical dialogue gets drowned out, too shrill, & it's painful. As has been pointed out, sub-woofer placement isn't critical, but if you place it in a corner, by nature of acoustic principles, it will boom unless you show restraint in it's volume level.
Now for the good news, I found a YouTube vid the other day from DIY Perks (I have him in My Favourites list), where he examined acoustic treatments, & he found that bath towels did a better job than the expensive acoustic panels: