Hello,
I agree with the above, I would try to make it work with a single row and maximize that and then have recliners (or those throw down cushion seats like fancy bean bags for younger folk with young backs) that can be brought in if you needed to expand in a moment's notice.
13 feet wide would likely handle 3 people comfortably, more than that and you're squeezing it in elbow to elbow. But, when you think about it, viewing distance for a 120" screen in a 17 foot room, you likely would sitting towards the back of the 17 foot room, but knowing your doors and access is back there, you cannot go too far back. So at least 3 feet of walk way room I assume back there, 3~4 feet of seating room, centered, and knowing your front equipment will take up at least 2 feet if not a little more from accessible room, leaves a viewing distance that is centered somewhere around 6~7 feet from the back wall and if you take 2 feet of room away with front equipment, you're got 8 feet or so from your seated position to the front mains. Getting crammed quickly since being too close to that 120" and you'll have to look left and right just to see the entire screen.
That 8 feet gets cut into deeply when you expand to two rows, knowing your back area cannot be flush to the wall, so another 3~4 feet of room and you're looking at being way too close to that 120" screen probably for comfort of viewing.
Tough choice!
Very best,