How many episodes in a season?
Not every season has the same number of episodes, but most are 14.
How long do they stay on the island?
39 days (except season 2 which was 42 days)
How long before it airs does it actually happen?
From the end of filming to the airing of the first episode is as short as around 2 months up to 6 or 7.
Does it air two seasons a year? Is that how it got to season (!!!)30 so fast?
Yes
Do the camera people and producers and stuff live on the island with them? Is it like Game of Thrones with three production teams on three separate locations?
They generally film at locations near a resort hotel or something like that. There is a AMA with a camera man from Survivor in the sidebar that goes into that kind of stuff than a lot more detail than I can.
What is the general structure of the show? I just started reading the subreddit, but I surmise that at some point there's a merge? And a tribe swap? And I figure like Big Brother at the end a jury of the last 7-9 evictees interrogate the finalists as to why they deserve to win and vote for the winner?
The structure varies from season to season to some degree. Most seasons have had two tribes while some have three (such as this one). Most seasons have a swap where players from the two tribes are mixed up (usually episode 5). The merge has happened anywhere from episode 7 to 10. Yes the jury is the last 7-9 people voted out usually the jury members are the first or second person out after the merge on ward, but there have been some exceptions.
Where would be the best way to watch the previous seasons? I don't need HD, 360p is good for me since my internet is way too slow anyway on the other side of the world. Big Brother had that quirkydude youtube channel and a torrent with all seasons at one point, is there something like that for Survivor?
There were a bunch of seasons on YouTube, but I heard a few weeks ago CBS pulled them all down. Depending if you have these things some or all seasons are available on CBS all access, Hulu Plus, Amazon Prime (I think), I've heard some websites have it, there are DVDs for a lot of seasons which you can get pretty cheap used, etc. etc. I'm sure google can help with this one.