An interesting point you make about the nominal ownership of a large part of John's fortune. It's possible that John has placed some properties in his wife's name for tax reasons, and given the mistake of doing so due to the possibility that she might take revenge on him if she discovered his numerous affairs, it wouldn't be a very smart move on his part, but I think it would fit perfectly within his arrogance and the fact that he's always considered her little more than a housewife and a trophy wife to show off at business dinners.
However, a person who is so easily willing to give large sums of money by surprise (like the $250,000 that MC gave in a briefcase to the Watsons on his first assignment) and Nicole's complete failure to mention that she usually signs papers because her husband asks her to, makes me suspect that if Nicole does have things in her name, John must have her express written authorization to do whatever he wants or that it is simply a matter of using her name for things that do not require her to know anything (for example, maybe John has some storage units rented in her name where he keeps objects or documents that he must keep hidden).
Most likely, if he is the sole owner of the real estate agency, he controls his fortune through its accounting (if I remember correctly, I think it has not been mentioned at all that the agency has its own accountant, perhaps because John himself has the authority to do so). In addition, he probably has his own accounts to cover non-legal expenses for his operations, such as those thugs he usually sends but that we only saw when Mr. Blues remembered what happened with John and his wife.
