I have a question here. lets say after HotS released and i want a new game account. I just buy HotS to get new account or need to buy WoL account first?

I'm pretty sure it's an expansion tied to the Wings of Liberty, not a stand-alone so yeah, you'll have to get Wings of Liberty first.

According to history... Both... You'll need a WOL in order for a HOTS to works... I think this applies to furthur installation.. you'll need a wol account activate a hots account... U'll might get a free name change thought...

i'm sensing ~3-4GB of extra patch for the new HoTS expansion should someone decided to get digital copy

If Blizzard stays true to how they've always done business, you'll need to buy HotS and LotV when they're released respectively and you'll need WoL and HotS to play LotV. You won't be able to skip HotS or just get either one of the expansions to play. There's a reason they call it an expansion..

I thought they mention it in their website that they will have another system for SEA since they introduced the 7 days pass if not mistaken.