Hey there!

Yeah, I'm afraid that's it. Terrain is certainly not even and it's a pain to plan out the palisade and the layout. I've started building houses in odd angles exactly because of that, because I couldn't find square areas with even terrain... so that's a pain, but it can be easily surpassed if you understand the wall building requirement. For segments of walls to be built, there can't be variation of more than 3 "ticks" of terrain level (the ticks you slide when using Survey Land). So you can use survey land to check the difference between the terrain levels although after the first few attempts you'll memorize the difference visually.
The trick is: you won't be able to extend big wall sections because of the difference but you can extend them tile by tile. So extend one tile, build, extend another tile, build, and so on... That's how I did it.
And yes, to make it work I have used roundpole fences. Just to make sure that the steepest parts were buildable. Still I failed in one point, and had to fix it by extending the wall a little further, here:

You can see that I've tried to make it a regular corner but couldn't build a wall on that "line" of terrain without snow... so I removed the paving and extended it a bit further...
So, yes, there's a lot of going around and work to do...
So don't give up now, the walls are the easy part

Here are some other screenshots showing how wavy and uneven my walls are and how I worked around some of the terrain complications (like cliffs) and such:



As for taking the "best spot", I highly doubt it.

First, I didn't walk around all the mountains in the world, just like 3 or 4...
And I *did* find some amazing spots on some of them, one of them was even better and more flat than this one - but it was too far away from other resources so I picked this up for convenience...
So there's no such thing as "having claimed" the best spot. It's a lot of work, yes. And it's not bad or wrong if you're not willing to start it all this late on the world

But if you do... well, this is all I can say

Good luck!
