Congratulations, Mike! And it sounds like you're off to a good start...blowing those secrets away hurts, but I think it's essential.
Before I get to your questions about NA, I have one question of my own. Have you thought about trying a medically-based program in addition to NA? A lot of US hospitals have intensive outpatient rehab programs (IOPs), and these can be very helpful (though admittedly their quality varies a lot). I think that when it comes to recovery, especially early on, getting *all* the help you can find/handle is a good starting point.
As for NA, there are a couple things you might be interested in knowing at this point.
First, different meetings are going to have different "personalities." I recommend shopping around the meetings in your area to find the ones that seem like they're populated by people you'd like to surround yourself with during recovery. I'd say the image you have of a seedy room full of dope fiends is not the norm for NA meetings, but if that's what you find (assuming that's not what you're after), keep looking. In my experience (about 2 years of lots of NA involvement), it's more typical to find the rooms full of people in pretty good spirits. There are likely to be some addicts right off the street. But there will probably be some professional and blue collar folks too.
During your first meetings, I don't think there's a right answer in terms of whether to share or not. If you're moved to share about what's going on, then by all means. But nobody will raise an eyebrow if you just listen.
One thing I do recommend, though it can be a little uncomfortable...at the beginning of each meeting, the chairperson will ask if there are any newcomers or people visiting. This is a good chance to simply raise speak up and say, "hey, I'm Mike and I'm new to NA. I'd be grateful to talk to folks after the meeting." Or something like that. If you don't want to announce that, at least do stick around after the meeting ends to try to talk to folks. The so-called "meeting after the meeting" is a great way to get into the community...it'll just be people standing around, smoking and talking. Very informal.
Another suggestion...the chairperson will ask if anyone would like a meeting list with other addicts' phone numbers. Ask for these as often as you care to. And try to use those phone numbers. This is a notoriously hard/awkward thing to do (cold-calling people). But for me, having that network of phone numbers is one of the best things about NA for people in early recovery. And keep in mind, people don't write their numbers on those lists unless they want people to call them...you won't be bothering anyone. Also, the calls can be brief and informal...along the lines of "hey, I was at a meeting with you the other day. I just wanted to say hey. My day today is going well/bad/hard [whatever fits.]"
The question about finding a sponsor is a tough one. And different people will have very different answers for you. *Personally* I would advise waiting a little while. Getting a bad sponsor match can be really discouraging, so I'd suggest waiting a little while until you have some ideas for whom you'd like to share your recovery with. As I said, though, other people would argue it's best to get a sponsor right away. The truth is, you can always switch sponsors if you find someone else you'd rather work with. But again, having had a bad match with my first sponsor, I think waiting a little while is a good plan.
One last thing...it's inevitable that there will be some jerks at most meetings. Frankly, sometimes there are even people at meetings simply looking for connections or similar. What all this means is that if you don't like the vibe you're getting from somebody, just excuse yourself and talk to someone else. And if anyone talks down to you (alas, some 12-step folks can be very bossy/dogmatic), just remember that they're just a peer and there's no need to take any bullshit to heart. Really all these cautions just suggest that it's healthy to keep in mind that there's no filter on who shows up to meetings and what they say, so you sometimes need to be a little skeptical.
Feel free to ask more questions here if you're unsure about any of this. That's why we're here!
Sim