The ultimate prize on offer is, of course, Lihua's hand in marriage. Nunnally receives final confirmation that the woman does indeed plan to take multiple husbands. It's both a salacious and unorthodox move, but little is traditional for China's first true Empress in over a thousand years. There is a hint of a blush to the young ruler's cheeks as she defers any commitment on this front, but she does state that any spouse she takes would need to demonstrate value to the Chinese Federation as a whole. From what Nunnally can glean, this means that, should her brother vie for Lihua's hand he can expect either some sort of top-level ministerial position or other responsibilities.
If Lelouch chooses not to take up a ministerial appointment, one of the 'other' responsibilities Lihua does not outright offer, but vaguely alludes to would be the governorship of the Indian subcontinent. Lelouch would be nominally beholden to Lihua, but largely under his own discretion as the highest military authority of the region. Lihua seems almost... too happy to nudge Nunnally towards this possibility, also offering up the idea that Lelouch could simply seize such a position without any 'material ties' to the political system of the Chinese Federation.
Very pointedly after the meeting is over, Kaguya also casually mentions a very large number with seven zeros on it as a personal income for the governor of India. It would be roughly analogous to an Area Governor of the Britannian Empire.
Working directly under the Empress in a ministerial position would actually have a less impressive income and more oversight given the arcane structure of the Federation's political system.
Nunnally cannot exactly ask to keep Guangzhou, but there are a few oblique questions she manages to pose as to who the Empress has in mind for a governor. The answer is suitably open-ended, strongly implying that Lelouch could push for such a position if he wanted. However, direct rule over one of the Chinese heartland's more profitable provinces as a foreigner, and foreign royalty at that... well, anything else would be far too much favor shown to such an interloper. Lihua even implies that such a position would need substantial smoothing over on her part to make others accept some non-specific foreign individual receiving it.
Nunnally is able to directly ask about aid in conquering Australia and the Empress is quick to affirm that, once this crisis is over a fleet, or even two, will be made available for Lelouch to force the pirates to bend the knee. This is a relatively modest favor to ask and one easily granted. On that note, it is also brought up that receiving a direct appointment and land to rule from a foreign sovereign would likely result in a conflict of interests with the Britannian throne. As such, the Empress could simply ask that Charles zi Britannia appoint his son as ambassador extraordinary and plenipotentiary to the Federation. Such an appointment would consume some of his time, but would also come with a healthy personal income that Lihua would be happy to supplement.
For the remainder of Lelouch's life.