Multitasking was not really a problem for Lex anymore. The ability to split his mind to have each mind focus on a different task made it so. Moreover, the current situation only required him to have two separate trains of thought running - one focused on the racing and one focused on the conversation in his office. For a moment, however, he had to create a third split to mercilessly beat down the rising greedy, capitalistic side of himself from emerging.
The thought of 300 million soldiers passing through his Inn, with more on the way, set his imagination wild for how much MP he could print. But the reason he had to rein himself in was that he wasn't logistically prepared to handle such volume.
All the systems he had in place would suddenly become overcrowded and overburdened. As much as he liked New York, the crowded subway at peak hour was not something he wanted to emulate.