Welcome to TBHP, Kiran! You have a very lucky Dad
The HU looks pretty good. Pretty much packed with features too.
Front: Good choice of front comps. They will fit in the front with a spacer. No issues there.
Rear: The stock provision in back allows for 6.5" speakers. Since you're going in for a sub, 6.5" will do. You can go for 6x9s with a spacer there, but they're really not necessary. Since you have GTO607c in front, a GTO637 (6.5" 2-way coaxial would be good in back).
Amp: Great choice of amp! Plus great options for the next upgrade (a mono amp later), if you plan one. You won't regret the purchase at all. I'd read on another thread than the 75.4 is temporarily out of stock all over, but should be available in the middle of June.
Sub: Go for the JBL GT4-12 (12" sub). It will fit the overall budget well, and will sound really good. Drop it in a sealed box and you're ready to rock.
BUDGET
Front Comps: 6.5K
Rear Coaxes: 4K
Amp: 13K
Sub: 5K
Box for sub: 1.5K
Power wiring (8AWG) and two 2-ch RCA interconnects: 5K (Audison/Stinger/Twister/Pyle/Other good brands). Note: Non-Audison (but still good enough) wiring will not run to more than 3.5 to 4K.
Damping: 5K (Front doors, boot, number plate, C pillar, roof)
Total: 40K
You will get tight bass from the GT-12 in a sealed box. The 75.4 will drive it pretty well and you shouldn't have complaints on that front.
Buying stuff from outside India may not always work out to be cheaper. Then there is always the inconvenience of lugging the equipment into India. You'll also need to pay extra for installation.