The Remote had the codes to access it, but with enough time and technical know how it could be sliced and activated that way. And I'm sure G0-T0 can procure some advanced slicer droids to do the job.
Of course, G0-T0 could just activate the Mass Shadow Generator, but doesn't that require Remote?
Concerning landing on Malachor, we have no evidence to suggest that Kreia guided the Hawk's descent. It could be that smaller ships that come to Malachor don't crash that often, or they do crash but are not destroyed. I'm sure G0-T0, if prepared, can plot a more steady descent (in my FanFic, I explained the to and froing of assassins from Malachor possible through use of special flight codes which plotted a course through the storms, pure speculation however.)
And fleets? What fleets? G0-T0 only has a yacht and possibly some freighters... I think ground forces are more important, and G0-T0 will have his factory locked down tight. So a ground battle is likely.
I'll leave are analysts (Aurbere and Wolf ) to consider that factor.