1 - how do you make lots of high mountains but not solid mountain ranges? with lots of X and Y variation? anybody have a sample?
2 - how do you make worlds colder (to get more glacier and frozen oceans) but still maintaining soil and rock layer variation and not getting lots of rejects? any paramater samples?
This post doesn't have any specific embarks, nor even any recipes, but it's general info on how to craft a recipe to get closer to what you want.
AFAIK, the general information on above ground world gen stuff is the same as it was in 40d. At least, it appears to behave the same, though I haven't had a chance to play around with it this summer. Check Advanced world generation in the wiki, the 40d article. To answer your questions based on that:
1 - Raise your X and Y variation, change the max and min elevation values to narrow the range of what's possible (do you really need peaks, high mountains and oceans?), set the mesh to the smallest size (the mesh size is the 'brush size' the engine uses to 'paint' features) and adjust your mesh ratios to emphasize the highest and lowest elevations (this part will need a lot of tweaking to taste). In my experience this works easiest if you forgo having any oceans (set minimum elevation above 99), but it should be tweakable to get what ever you want. You can find the elevation values for various biomes on the wiki. Be aware that variation numbers scale oddly with respect to map size. 800 variation on a pocket sized map will produce a lot of variation, on a large map not so much. I suspect what is happening is that the mesh sizes scale up along with the map size, so it's harder to get micro changes on a larger map. That's okay, the variation limits in game are soft limits, the engine can deal with much higher numbers, so you'll need to change the world gen recipe by hand. The main ones to change are the variation numbers (for a large world with what you want, start at 6400 and experiment from there) and the subregion (make it at least 50000). A word of warning, you will likely get a lot of rejects for not having enough mountain regions, even with minimum regions set to none. Just tell the game to ignore those rejects and continue, you'll still have plenty of mountains and you need to see an end result in order to tweak your recipe.
2 - The poles will be your max and min temperature values. You can adjust the mesh sizes and ratios to tailor the temp transition. I'd check the wiki for the appropriate values, set your temp the the range you want and change the mesh ratios to emphasize the colder temps. I don't really know anything about layer variation and cold temps, but soil doesn't appear under glaciers. Also, taigas are not freezing biomes, so you have to allow for warmer than freezing temperatures to get taigas (and liquid water).
You're probably going to get a lot of rejects no matter what. That's okay. The whole process can be extremely time consuming, especially as the world size scaling means that it's very difficult to test out a set of parameters with a small world then translate that recipe to a large one. But that's okay, if your willing to take the time you'll eventually end up with a recipe that'll provide you with dozens of appropriate embarks basically every time you run it*. I'd suggest checking out the old worldgen cookbook thread and copying over the essential elements of any recipe that looks promising as a starting point.
For flat embarks, set the elevation mesh to as large as possible, keep the variation low (maybe 200 for a large world, 20 or so for a pocket?), and adjust the elevation range to only include the terrain features that you want. 279-320 should give you equal amounts of grassland/forest/swamp/'hills' and low mountains and nothing else. It'll also give a lot of rejects. If you don't want hills (which can still be flat) keep your drainage below 50. That'll
probably work for pretty much any map size.
*Depending on what you're looking for. The parameters are quite powerful, once you know what they're about, but things like a volcano on an ocean shore are trickier. For that I'd suggest a lot of volcanoes coupled with elevation restrictions that keep the over all height of the map low. The hard bit is keeping the land all joined up so you have access to civs...