Biju,
is the room 15 ft or 15 m? what is the width of the room?
Just to give you an idea, I have a 13 ft x 20 ft room. My front speakers are studio monitors and have the ports in front. I ended up building a wood frame and installed it 18" in front of the front wall. Put the speakers behind it. The 18" was just to clear the speakers, after towed in. The front wall was treated with acoustic material to absorb the reflections from back wall. The screen was SeymourAV centerstage XD and was mounted on the wood frame in front of the speakers. This ended up reducing the length of the room by 18" but worth it.
As for your setup, since its a theater, I would suggest you go with 7.x setup. Instead of floorstanders for fronts, go with high quality bookshelf speakers. I like the Infinity Primus P163, if you can source them. They are quite cheap but very good quality. In fact, you can have 7 of them.
AVR - There are some good advice at this forum on AVR's. at lower end, I prefer Yamaha Aventage receivers. Then there are denon, Marantz, Onkyo etc. Just pick one that meets your budget. Get an avr with good room correction, pre-outs etc. You can add an amp later if you have pre-out.
Amp - Not necessarily. Run with the AVR. that will have enough juice.
Bluray player - get whichever you prefer.
Cables - Monoprice cable. For HDMI, see if you can get HDMI over ethernet. that way you won't have to worry about it becoming obsolete when new HDMI version comes out. Or at least get Redmere spec HDMI cable.