If you were to have a 24 ft. projector-to-screen throw distance (this is from the front of the projector's lens to the screen) then projectors such as an Epson 5010 would require a screen size of at least 120 inches diagonal (in 16 x 9 format). If you need to mount it with a 10% longer throw distance then your minimum screen size would be 10% bigger, etc. Be aware you would get the maximum image brightness (i.e., max. lumens out of the projector) when it is positioned for minimum throw distance and using a max. throw distance can reduce the projector's light output by as much as 50%, depending on the specific projector model. In the case of the Epson 5010 (for example), the light output when used at maximum throw distance (i.e., minimum zoom) is only about 2/3 as much as it is when used at minimum throw distance (i.e., maximum zoom). The Epson 5010 should have enough lumens output (in a fairly accurate color mode) to give good results for viewing standard 2D movies/video and an acceptably bright image for 3D. However, using a screen with some gain (1.3 or higher) would certainly benefit 3D viewing and if you could mount the projector at only 50" to 60" above floor level then a Da-lite High Power screen, with a gain of 2.4, could work well.