When thinking of the 747 for FSX there is only 2 that spring to mind, CLS 747 and PMDG747, there might be a decent freeware version of it from Project Opensky but not sure, check the libraries at AVSIM & Flightsim.
CLS747 is cheaper but less detailed (I use it and fairly happy with it) and although a more complex flight model then the default FSX 747 it pretty basic compared to the immensely detailed PMDG. The PMDG 747 is much much more expensive, especially as they have several different models which have a hefty price tag each! But then again, they are seriously indepth.
As for HD or even UHDT liveries, alas none of them have it. McPhat, the only company doing UHDT, have only done UHDT on the Super 80s and CS757 series. They have also done HD liveries for PMDG's MD-11 just recently. Some other companies are slowly venturing out into HD livery territory like Carenado's Grand Caravan and the 2 recent releases of Captain Sim, the B-52 & B707 are both in HD paintkit format.
Best thing would be to check reviews & pricing on both the CLS & PMDG's version, AVSIM best place for reviews. Oh and CLS's 747 is rather old now and doesn't run in DX10 mode.
That's all I can think of.
Cheers.