I think these two statements say it best. Revan takes over the Republic with minimal casualties, adding them to his side. With the Republic Navy as his resources for warm bodies, and the Star Forge for everything else, he would use the grand army to strike at the True Sith, who wouldn't stand much of a chance against Revan's near-limitless Republic troops, crewmen, and pilots, and the limitless Star Forge ships, starfighters, and droids.
The biggest problem with the Republic would be dissent, which would do nothing but slow him down (there are enough political efficiency jokes out there), which is why he needed to depower the Republic leadership (Supreme Chancellor and Senate), so his will would become action.
How ruthless he would be in his command, I would have no idea...