Welcome to AudioCircle, Anand!
If I was designing a speaker to use your parts my thinking would go like this:
Good drivers and electronics! You can make a fine speaker with those! The 18" woofer can provide enough punch if you feed it enough power. It has Qts of .38 so it has good self damping properties for tight bass. You will have to apply a lot of boost to it with the DSP, but it can handle the power and the 500W hypex is capable. Use a test signal and SPL meter on smart phone to apply bass boost as desired.
I would use a 24 x 48" plywood baffle. Put the woofer on center, so that the bottom edge is 1" away from floor. Put the TB at 40" above the floor (ear height) and center of hole is at 1/3 of baffle width (not centered) for flatter frequency response.
Apply some kind of bracing or damping strategy to prevent baffle vibration which colors the sound.
Tilt the baffle back so the beaming treble from the TB will shoot over your head.
Use 24dB/octave crossover filters at 150Hz to start. Adjust this xo frequency to adjust the "thickness" sound in the midbass to your liking.
There's lots of good help here so bring all your questions as you go along.
