I was wondering if anyone knows if there will be any problems with me adding events to my wishlist for the same time slot.  There are several RPG's I wish to play in, but I know from that past that it is hard to get into many of these games.   I want to register for 3 different games which start at the same time, in the hope that I may get into one of them.

Will the registration system allow me to do this, or will it give me an error message when I try to submit the wish list?

I'm pretty sure it won't let you when you submit your wishlist. I had a similar problem last year. 

You can submit as many items that overlap on your wishlist as you want.  The way it works is that your wishlist's item #1 is processed, then item #2, and so on, skipping any event that overlaps one you already have a ticket for.

If you want to have three different games that start at, say, noon on Friday, you can do so, but be sure they are in the order of most wanted to least wanted.

Yup, that's absolutely what you do; you put your top three choices for events for a specific time slot on your wish list in the order of preference, and it'll go through them until it finds tickets for an event you that has tickets you want; it'll check 1, then 2, then 3, and once it has tickets for a time slot it will skip over other events at that same time.