What sort of image?
If you want a computer image that says Merry Christmas and Happy New Year, all you need is adequate brightness.
If you want to project a movie from DVD or BD, ask studio first and obtain permission.
Movies look better on a smoothly plastered surface and for this purpose you might get an estimate before purchase of projector.
If you want to try plastering yourself, go to Home Depot and tell them you want to plaster a wall. If this is your first plaster job, try a small portion, maybe 6 ft tall by 10 ft wide. From this experience, you can determine if you can handle a larger job and extimate how long you may need. You need time estimate to rent scafolding and come up with reasonable cost estimate.