Sorry for the late reply. I do not know how accurate the figures are for the SU-34, but it is a heavier aircraft with larger cockpit, titanium tub, larger reinforced landing gear and additional avionics so it should weigh more than the MKI, the heavier the aircraft is the less munitions it will take. So to be honest I do not know the figures and I do not know if I trust internet figures since some can be wrong or outdated.
As for storing weapons internally inside the SU-34, of course this can be done but it would be a lot of work and a lot of money, and if the designers go as so far as to incorporate weapons bays than I would imagine that they would go a step further and add other features to reduce RCS. Now in regards to the nose, my guess is that it is a result of the tandem cockpit, in other words it was the best design choice. The plus side is that it may very well have a lower RCS as a result.
Pave PAWS operates in the mhz -- meters length -- bands. The X-band is simply too weak to reach that four-digits km distance. Currently, the Pave PAWS systems are located in Mass. and Calif. They are for sea launch ICBM warnings. There are other long range radar stations that includes Alas. but Pave PAWS is not part of them. And yes, they are operational.