I am trying to make a square size video of 6:5.
Is your video square or is your video already 6:5?
The size of the screen is 12feet x 10feet
The screen has a 6:5 ratio, so your video will fit.
But if your video is really square, let's say 1000x1000px, you simply need to crop it.
pixels it's 13824x11520p.
No, do not resample any video.
@stib already mentioned it. You would need a very powerful computer to playback that. But there are some other elements.
A screen of 12x10 feet is meant to be watched at a distance. Here is an example. You are in a movie theater. The screen can be bigger in size than 12 feet, and you do not use a humungous resolution because you do not need it, not at all. A 4K image is more than enough. Actually a Full HD image is probably good enough. Not even an IMAX laser projector has the resolution you are talking about.
Any resampling you make will produce... a resampled video. You will not introduce any sharper detail or anything, you will simply turn your video in the exact same video but a heck lot bulkier. The resampling needs to be done in the hardware of the screen. It will probably simply multiply the information to be projected into the different zones of the screen.