For a 100" screen optimal viewing Distance is 13'. For your pj, if it can handle that distance then you can mount the pj directly over or a bit at the back of your head so you wont get distracted when watching.
Now if later on you would want a bigger screen than 100" then this early you have to compute for it, 120"-140" may require pj distance of 12'-16' depending on model of pj. But Keep in mind the closer the pj to the screen the better for the lamp power(lumens)
Congrats on your pj sir