^^ ok so the HT room stands at original 15x10x8 ...right..........and for music I should change it to 10x9x8....
Yes

Also can you assist me in selecting center and SUB, or may be just center as I am struggling for a compatible center under my budget.
Everything else is ordered and on it way....
I know nothing about HT setups, really. Except for the generic info that the center should be the same as the fronts, I really have no idea about choosing a center channel, sorry

About the sub also, I know very little, but I've listened to a Velodyne Impact 12 in a HT setup (the room was 12 x 16 x 10, or very close to it) and it sounded quite good. I think it is between 25K and 30K. It may not do a very good job with music, though. You should get a Velodyne Impact 10 for around 25K.
If you have a more generous budget for a sub, say north of 60K, something from SVS would be excellent. I'm not sure of pricing, but a PB12NSD would be something like 70K, I think. It should do a fair job with music also, if you'd like it to multi-task. Audire (Coimbatore) deals in SVS. For music only, I'd get a Rel T5 (50-55K, I think).