I wouldn't jump to that conclusion so quickly. Yes Revan fights on the front lines but in this situation there are no 'front lines'. Xizor can only muster a large enough fleet to wage a shadow war, and any open tactics will be hit and run, too fast for Revan to react personally. Most of his fleet will be stationary, and Revan can't zip about from one side of the galaxy to another dealing personally with everyone of Xizor's strikes, especially seeing as Xizor is trying to assassinate him.
1.) Lock-down on Lehon
Makes no sense to the character. Revan would never do this. He's too strong, too driven, and too much of a figurehead to retreat. The last time he was in a war, was he hiding? No, he was on the front lines. Commanding from his flagship, not from some meditation chamber. He didn't hide from Jedi, there's no way he's hiding from criminals. Arguments that don't make sense to the character would never happen, and so shouldn't be evaluated.
However as Lehon is in the Unknown Regions Revan would not be able to respond rapidly to any matters that needed his attention and communications would be difficult. So if anything it will be a last resort. But still a possibility. Its the first place Revan will go if he escapes a failed assassination attempt. Lets also remember that Revan is cold and calculating, and a celebrated tactician. He can put aside his 'strong and driven' persona for the sake of practicality and survival.
However because he is not waging full scale war, and because he needs to keep in contact and command of his forces, he very well may simply station a large fleet above Korriban and command his forces from there. Or from another stronghold - which would make it very difficult for Xizor to permeate. And given the 'low-key' status of the war, little if any resupplying and refueling will be carried out. We also have to consider that Revan will realise he is being boarded no matter how they infiltrate the ship (especially if they cut through his hull) and will respond accordingly. First step: get off the ship, second step: defend the engines etc. from sabotage. We have the remember the flagship will be swarming with Sith assassins, dark Jedi, Sith troopers, battle droids etc.
And concerning Revan's flagship, we can assume it had the same specs as the Leviathan which was an upgraded version of the Interdictor. So lets just say 75% of an Imperial II-Class Star Destroyer.
However concerning Xizor. No one has put forward a powerful argument as to how Revan will kill him/track him down. If he escapes Coruscant this could become very difficult.