wat is ur budget?maybe can drop me pm. i have some nice for sell

Here is the questions:
1) How do i determine what minimum specification is required to power up a single Subwoofer (e.g. 1500W)?
- depends on specs of amp or specs of sub, which ever u get first, in watts rms, not max
2) How can i bridge a 2 Ch Amp, as in which + and - teminal to choose? (e.g. 1st Ch (-) with 2nd Ch (+) or vice versa)?
if the sub is single voice coil then its straightforward, +ve from one channel and -ve from the other channel.  if its double voice coil then theres parallel or series connection, which u can google for diagrams
3) What will happen if the amp specifications is LOWER or HIGHER than the minumum requirements to power up the subwoofer?
preferably look for something 50% more than sub's rated rms power, look at amp's bridged mono power rms specs.
more importantly is to keep the amp's gain level below distortion level

zenn means rms X 1.5
i'd say rms X 1.3 is enuf
700 X 1.3 = 910w rms

always look at rms/nominal ratings.
peak/max ratings dun mean anything.

it is ok... but you loose the RCA signal strength when you do that...

Pros:
1. you could still get music for all the amps you connect it to.

Cons:
1. Low signal strength means higher gain from amp which means possible of distortions.
2. no fader control.
3. if your amp doesnt have a built in x-over you will have trouble getting the sound right.

Its either printed RMS or PMPO...if none..just ignore it..find something that is clearly stated...makes life alot easy.

I think it'll be safe to say, if you stick with the better brands, just take note of the Watt RMS rating. Most of the Watt ratings printed largely on the amp/sub itself could most probably be MAX PMPO and not RMS.

As for a matching amp, for example, if you have a sub that's about 100WRMS, try getting a 150WRMS or 200WRMS per channel amp to pair with it but you have to be mindful of the correct gain settings.

Personally though, if your HU only has a pair of RCA outputs, you would be better off upgrading to a 2-channel amp with a pair of decent ready-matched component set, or if your budget permits, get a 4-channel amp, a pair of components, and a subwoofer.

If you still ain't satisfied down the road, then only you upgrade your HU with at least 2-pairs of RCA outputs for better control of fader or crossover settings.

Personally, I would always say if you gonna upgrade HU, at least get a decent one with at least 2-pairs of HU or you'll spend more down the road. Like the saying goes "The Poor Man Pays Twice"