In order for anyone to be a good moderator, they need to know what is expected of the moderators at this particular site, and they need to feel that they want the same thins as the other moderators and the site owner.
So the first thing you need to consider is what you want from the site. Why did you start the wiki in the first place? What did you want to achieve? What sort of users did you want on the site, and did you succeed in attracting those users? If you haven't got those things clear, you really need to start thinking about it before you bring others in as co-admins/moderators.
Once you've got this clear, you need to think about what the terms of moderation are. What is it you expect the moderators to do? What kinds of decisions will they have to make, and how do you want the moderators to make them? What community rules and/or guidelines do you have at this point, and how do you usually enforce them? Again, these are things that you really need to be clear about. If you don't know what you want the moderators to do and how they should do it, there is no way that they will be able to consistently do what you want.
You also need to figure out how you want to deal with any problems with the moderators themselves. What will you do if someone doesn't enforce and/or abide by the guidelines? What will you do when there's a disagreement between the moderators? What powers should the moderators have against one another as well as against the users?
Now that you have clear guidelines and a clear view of how you want the moderators to work, you can start thinking about who you'd like to be a moderator. Since you've got a lot invested in the site, and you'll still be doing the lion's share of the work for some time, you should pick people that you feel you can communicate well with and who appear to have the same ideals as yourself as regards the site. They should behave towards others in the way you think is the best possible way to act on the site. If possible, choose people from more than one timezone; it will reduce the time people will have to wait for a moderator to handle a problem.
The most important thing, though - if there's a user who's done something less than stellar, maybe said something rude or stepped on somebody's toes... have a look at how they handled it. You want someone who is open to the suggestion that they may have made a mistake, who kept their temper when challenged, and who was ready to apologize and change their behaviour when in the wrong. This is the most important skill for anybody who is in effect representing you on your site.
You also need to remember that no choice is irrevocable. You need to be prepared both for the moderators to resign for whatever reason, and for you to need to kick someone off the team when necessary. Make sure you have already thought about how to handle this when it happens.