WOW Rajesh, that is a BIG room!!!...You have an ideal seup for a CIH Cinemascope screen..
If your first row is at 20', then you're going to need a VERY wide screen and a light cannon of a projector..
In that width room you could easily fit a 15' wide screen..With a Scope screen, that would give you a 6' high screen, giving a diagonal of 16'..
That would give a seating to screen width ratio of 1.3:1 for the first row, which is nearly ideal for a Scope screen..
I can't help you with the best projector for that situation, but one thing I do recommend with a screen of that size is to look at using an acoustically transparent screen and placing your speakers behind the screen..
For the Anamorphic lens I would suggest that your going to need a very high quality unit and one of the best are the ISCO range of lenses, but very expensive..
Keep us up to date with your progress..