Noted and thanks. See below.
Correct... controlling ambient light is paramount...living room is not ideal but can be managed via black-out curtains, ambient light rejection screen, etc. Reflected light from the screen needs to be managed too. The room doesn't have to be pitch black, obviously the darker the better.
You can maintain a TV for day use, and projector for movie night

*** Plan to upgrade only after my TV is about to RIP. Ha. Prefer to have only one.
Lamp replacement frequency is a non-issue IMHO. My projectors are rated 6000 hrs in eco/low power mode. It means at 6000 hrs, light output is reduced by half. I put mine in eco because they are still quite bright, and when time comes I can crank it back up for extra say 1000hrs... if you use 2 hrs per day, 6000 hrs == 8 years!
*** My family usage is easily 8-12 hrs per day!
Bare bulb costs US$ 20-30 for DIY...buying the whole light housing will obviously cost a bit more, on Lazada < RM300.
AA. For now LCoS is regarded the "best" for black level but expensive...not sure if Sony has fixed their degradation issue, so only JVC is recommended. LCD tech has improved a lot...look towards Epson, Panasonic has been quiet. "Cheap" native 4K DLP from Optoma has just been launched, FHD DLP from Optoma, Benq, are quite good too. So really depends what is important to you...a "con" may be immaterial for your usage...
BB. White/light gray is best for a dark room. Your case may call for an ambient light rejection screen...the grayness and gain depends on how bright your room and projector are...good ones are not cheap so most folks are better off with black-out curtains.
CC. 1080p projector, 3.5k to 20k, mid range 6-8k. Screen, 1k to 10k. What's in your wallet?
*** Around RM10K for a changeover.
P/S I assume TV tech cycle is around 3-6 yrs, new tech comes out like the HDR and 10 bits colour. What about projector? They change frequently? Hope not as it will be a struggle/poison with new features coming out every few months.