I’m just getting started too. It would seem with 4” high and 50” you will have quite a bit of room to work with. BTW, 4’ seems a bit tall maybe. Of course it depends upon how tall you are and how tall the people who might use it are. I found a company that makes standing desks and on their website the suggest for someone 5’ 11” to order a desk 44” tall. With desks, countertops, etc. the ergonomics on even an inch or two really makes astounding differences. So check that carefully.
I found this calculator which seems helpful to me. Although I haven’t built anything with it yet:
For my projector it says that 50” diagonal will take a throw of 5’ 5”. So to build it with a Toshiba TLP-XC2000U (what I got) you would need a mirror to bounce the beam.
There are short throw projectors that I’ve seen mentioned in the forums. Of course most of those seem to be more expensive thant I wanted to pay, $600+. (US dollars. I don’t know where you are.) Somebody was using the BenQ MP512ST and it would only take 3 feet to get a 50” image.
Not that I am specifically endorsing either of these projectors. It is just some of the stuff I’ve seen here on the forums. It really is going to come down to which projector you can find at a price you are willing to pay.
The other thing I like about this calculator is that it has a suggested ambient lighting gradient as well.