sometimes it's just a matter of hitting the tire with enough psi to set the bead, tires are stacked, pressed and banded before shipping and it can deform the carcass. removing the valve from the stem and hitting it with 120 lbs should do the trick. or there's always the old starting fluid and throw matches at it trick, which i've used before with success. if the bead seat is that corroded (on mag, it will be white powdery appearance) then you may want to try and polish the surface up, provided that the pitting isnt too deep.
as far as a tube goes, if the wheel is balanced after assembly then there wont be any out of balance issues.