reply is mostly to bakara guru,
I retired from WoW 6 months ago or so, and I went through a lot of the same stuff you did. I was a veteran player from the early days who quit then came back to all these new features. So after getting a couple 80's, I tried all the new "weekly raid", "pug raids" etc. I found that the biggest issue facing these raids is that since there are so many players out there, they are forced to base everything off of your gear and whether or not you have the achievement. Addons like "gearscore" make this easy for them to judge a player by. I found because of this, it was hard to get into the raids at first...
However, after you get all the gear you can from the 5 man heroic badges, you will be ready to go with any sort of raid. I would say, even ICC if you can find one. Then, your issue shifts from being "undergeared" to being "inexperienced", because a lot of times people want you to show you the achievement, proving you already did it. I found that silly, because it really limits the pool of people available, and when you finally get to run these raids, you'll see it isn't rocket science. You'll be like, wow, this is easier than everyone made it sound.
I guess people want a way of weeding out morons. I think showing achievement wasn't really a good way, but I guess it gives people peace of mind knowing that they won't have to explain everything.
You seem like a smart guy and you do your research on websites, which is more than the vast majority of these players do. I think you will be fine in any of these raids, as long you can are persistent enough to get into them. Finding a good guild that can run raids is an easier way to do it.
In the end, I think that running nothing but pugs was what made me quit again. I never really made many friends in the game the second time around, never got into a good guild, and I ended up quitting again. It's the friendships that kept me around for a long time when I played in the early days. However, the new mechanics of the game make it very easy to be successful without even trying to be social, which I feel lowered my desire to keep going in the end. Pretty sad that I need to be forced to be social, eh?
Anyway, good luck!