I've had a PJ theatre for the past 28 years, so I know the basics. Yes you'll need a receiver, Sub (at least one) a center channel speaker, (spend some money on this, as you'll hear it more than the other speakers in your set up). and a PJ and screen. The two PJs you list, I'm assuming was based on budget correct? Before you make a choice on a PJ you need to figure out if you are affected by the Rainbow Effect. This is the sensation of seeing Rainbow patterns in the screen in high contrast scenes (think black and white) and high speed motion scenes. This can become a big deal when you are watching a 120 inch screen and your eyes need to move back and forth rapidly from one side of the screen to the other to see what is going on. It is during this motion that you will see the rainbows... if you do. As someone that does, it can be very irritating. The first PJ you linked is a DLP. The DLP technology uses a spinning wheel with multiple color segments that the light shines through. This is what causes the rainbow effect.
The second PJ you linked uses a system that shines the light through a transparent LCD screen to make the picture. This technology does not have rainbow effect.
Find out this answer before you proceed with a PJ purchase. I have always used a traditional 3 gun Red Green Blue CRT PJ,( currently a Marquee 9500) because I am so affected by the rainbow, but my next PJ will probably be a 3LCD, unless laser becomes affordable enough to go that route. The CRT PJs are not capable of throwing a 4k pic, that's why I will eventually move over. Depending on your budget you may want to look into a 4k PJ simply because most of them on the market up convert video signals to improve the native picture which helps when you are watching 120 inches.
Most new DLP and 3LCD PJs will be bright enough for that room. You want at least 2000+ lumens for that bright of a room... Consider black out shades as well....
Lastly research the best screen you can afford. It doesn't need to be really expensive, but make sure it compliments your PJ.
Good luck on your theatre.... you will never want to go back, and if you're like me you will never want to go out to a theater again.
Hope this helps.