Ok, been playing this game fairly obsessively for a couple of weeks now. I've yet to ever get a siege. In fact, most every Fortress I found is hopelessly undangerous. I've been putting myself in Terrifying places and Untamed Wilds, but the only 'mean' critters I ever get are some rhesus macaques and slugmen/snailmen. I get a lot of those.
How do I get a place with some dangerous critters? If I wait long enough, do they just show up?
Unfortunately, there's no way of knowing exactly what wildlife awaits you until you strike the earth, so it's pretty much hit or miss. If you want better siege odds, try the orc mod.
Also, I did a 'find' looking for a magma pipe. It gives me a place and I've just about mined out the entire underground spit and can't find the damn pipe anywhere. Is it guaranteed to exist on the spot the 'find' thing gives you?
If the finder said "Suitable Site", then yes. If it said "Partial Match", then no.
Also, on the screen where you pick your spot to build, I look in the 'civilizations' screen. Sometimes I see goblins and they had a red dotted line next to them. What does that mean?
It means they're trying to kill you, as normal. If you don't see them, they can't reach you.
I settled on a goblin fortress once, and they were all friendly, and had humans all over the place. Human priests and stuff. What's up with that?
The friendly goblins is a bug in the current version, where intelligent creatures that already live at your embark site are friendly. The humans were snatched as babies, goblin forts tend to have large populations of non-goblin residents.
I want to settle in a fairly dangerous place, so I have something other than just building what I wanna build to take into account. How do I get that?
Like I said, orcs. If you throw in a few extra copies of the entity with different active seasons, you're more likely to be at war with at least one of them, and there's a good chance you can get sieged every season.