Oh yes indeed, Rassilon does have a new Tardis commissioned, though I doubt he ever uses it but to observe the battlefield of the time war early on..I can't see rassilon himself fighting with a tardis, unless he knew he could win without harm to himself.
I don't know about that... Rassilon being biologically immortal and creator of the Eye of Harmony, with his extreme megalomania on top of all that leads me to think he believed himself a living omnipotent god.
I see evidence from 'The End of Time' pointing to this also. Remember he said: "I will not
die!". In the context of the time lady's treacherous suggestion, what Rassilon meant was that he would not choose
death. He also lead the return of the Time Lords to earth to confront the Doctor and the Master, both of whom were possibly considered the most dangerous beings alive next to himself and Omega. In my mind, this was hardly a man who thought anything had the power to threaten him. After all, It was his overconfidence that led to his destruction.
And how better to demonstrate one's overconfidence than by materialising onto the battlefield in a monster of a war Tardis, dwarfing entire fleets and erasing whole Dalek planets with D-Mat guns?