>>1.Given the above criteria, what is the minimum room size (WxL) that is necessary?
That depends on the answer to (2), and if you're using an acoustically transparent screen (which adds 2-3' depth). Assuming an AT screen with 2' deep false wall, three rows of recliners spaced 7' apart, and 11' first row seating to screen distance, it would be 27' or so long. My room with 4 across curved seats in the back is 17' wide, and that works pretty well, still enough room on both sides. So maybe 27'x17'. If you use barstools in the back row, you can deal with just one riser (bar stools sit higher than the recliners on the same level), and cut down on room depth a couple feet.
>>2.How far apart should each row be from the other?
That depends on the type of seats - if recliners, figure about 7' between rows to allow for recline and ability to get to/from your seat. If not recliners (typical movie theater seats, or couches, etc.), will be less.
>>3.How high should each step be? Is a 6" step enough?
That depends on how high your screen is mounted. There is a riser height calculator that you can use to estimate; mine ended up being 12" high for the second row, which was just enough to be able to see the bottom of the screen from the second row, over the seats and heads in the first.
>>4.Any other details that is necessary for us to know at the planning stage?
One thing that comes to mind is you may need multiple side surrounds to provide adequate coverage for the three rows.
Have you considered using the Pro Layout Service
? Take a look at least. Although I am happy where I ended up with my build, my build would have been accelerated significantly if that service had been available at the time - a lot of time spent researching and waffling on decisions, vs. following a well thought out plan.
Also, take some time to browse through some of the more popular (# of posts, # of views) build threads here for ideas, you'll pick up a lot of ideas that you might not have considered, that you can integrate into your plan.