A 100" 16:9 fixed screen will be approximately 94" wide including the frame, which is over 7.5 feet by 4 plus inches... Then there are speakers to be placed up front also. So, if your going to have the screen on the small wall you will probably have to go with a 90" diagonal screen. Since your trying to maximize screen it would be recommended to create a false wall with an AT screen so you can put all the speakers behind the screen. This will take up a few feet of distance in the room but allow you to maximize the screen and hide the front speakers for a cleaner look.
Your front row of seats should be around 10 feet from the screen (100" screen) IMO. Since you possibly will be going with a 90" screen you can probably scoot the front row of seats up a few feet, maybe 8 feet. It will be a tight fit with two rows of seats. You will have to shop for the right kind to fit, most likely not have recliners in the second row as not enough space.
Recommend you leave a few feet of distance from the wall to the back row for rear speakers. Other options are ceiling mounted rears etc.
You can make the room work, just have to be creative and realize the limits your working with (room dimensions).
Some may say put the screen on the longer wall, IMO it does you no good to use the big wall for the screen as you would seriously limit your sitting distance (and a second row) and wouldn't be able to take advantage of a larger screen. That is unless your gonna be headwhipping side to side to see the screen.