I think an AI with a traveling home node is not necessarily an unworkable character concept; yes, it does put you more at risk, but you're still not in as much danger as your meatbag teammates, who are also directly in the line of fire and don't have the advantage of being made of metal. (Also, I posit that no one's going to assume you're sentient unless they're given fairly convincing evidence otherwise.) If you're really attached to the limo thing, go for it -- off the top of my head, I can't think of those exact stats from any of the sourcebooks, so you might have to work with your GM to adapt one of the existing vehicles. I might also consider something smaller, though; you'll probably be living in a nexus, which is about the size of a computer tower and thus fairly portable. If you picked the car because you wanted to be where the action is (and/or have a GM who won't allow a completely hands-off character, always a possibility) you could throw your home node in something that fits through doors a little better than a limousine.
