I just set up two people who I really, really like! I am so excited and curious, but I don't want to follow up too much. What do you suggest in terms of my role now that I've made the initial introduction?
Isn't it an awesome feeling, knowing that two people who you like may also end up liking, and maybe even loving, each other?! People often tell me how helpful and selfless it is of me to play matchmaker, but honestly, I get a total thrill out of it, and it sounds like you do, too.
As much as it's great to enjoy the experience as the matchmaker, your job now is to be the intermediary for the potential couple. Create whatever wedding fantasies you want in your head (including, of course, the toast where they thank you for changing their lives), but keep your actual interactions with them focused on their needs, not yours.
If you've only just introduced them over email and don't yet know if they've talked or gone out, you could follow up with one or both of them to ask, "Have you been able to connect yet with so and so? No pressure, I'm just really excited for you to meet and wanted to know if there was anything I can do to help."
This way, if one of them has reached out and hasn't heard back, you provide a comfortable way to ask for intervention. If they've already set up a date, you can say, "Wonderful! I can't wait to hear how it goes."
If you don't hear back after the date, feel free to follow up again to say, "I know you went out this week, and I just wanted to check in." You're not asking for juicy details, but you're making yourself available.
The most important question I ask myself after a set up is, "What will be helpful to these two people?" If I ask the daters, "Tell me what you found interesting about him/her," that could facilitate a forum for processing the experience. If I ask, "Where did he take you for dinner?" that's most likely just feeding my own desire for details.
Depending on your relationship with each of the people you set up, it may be more natural to talk about physical attraction with one than the other, or it may make more sense to compare the experience to previous dates if you know his/her dating history well enough. Overall, you want to be supportive without being nosy and interested without being judgemental.
If it turns out that one wants a second date and the other doesn't, or that one doesn't know how to proceed, you may find yourself in a very delicate but extremely important position. No one likes to be rejected, but, as a mutual friend, you may be able to soften the blow while also saying something like, "I'm so sorry this one didn't work out, but I think I have a better idea now of your type, and I'll keep you in mind for other possible set ups."
If things do work out (yay!), after a second or third date, the situation isn't about you anymore. You shouldn't expect any more updates until they either break up or get engaged. You can continue to talk to your friends, of course, but don't keep reminding them that you're responsible for the set-up (especially if they break up!). Just be the gracious and kind friend who thought to set them up in the first place. If you're lucky, there may yet be a wedding toast to you in the future.