Oh my god! What is TSK sir upto? LBM effect?
On a serious note, I think you should get in touch with Sam, Gunman, JB, B&T or Navin and discuss this in detail for the best.
Regarding the HU, do you require one with B&W? Or grey is fine?
By 4 speakers, I think you mean a component kit. Right? Yes, the one which comes with 2 uffers and 2 tutors.
You can power your sub using a 2channel amp. Yes, a 60.2 will do the job. But if You're getting a powerful sub later, then this won't suffice.
And if You're getting a component kit which comes with seperate crossovers (every component kit comes with some kind of these, so you don't have to buy another one of these for now), then it is possible to power the tweeters from the front channel of the HU and woofers from the rear channels. This will make them play good. If they don't have seperate crossovers for tweeters and woofers, then you will have to either play from just the rear or front channels of the HU.
Best bet is to get a 4 channel amp like the 60.4 or so and Power the fronts and sub from it.
There are some nice deals in the market area. Keep an eye on those.
You don't need to buy HPF. It comes in the HU and Amp.
You can avoid the rear speakers if You're not very keen on it.