I've tried for hours and hours to gen this site using my crude, inadequate understanding of worldgen parameters, finally got lucky and found a suitable site, only to have the save become corrupt and unusable.
(running mayday's 40d16 package, if that makes a difference)
The challenge-
3x3 embark with
joyous wilds
heavily forested
magma pool
sedimentary flux layer(coal/magnetite)
nonevaporating water(so I can turn off weather and temp and still have water for injured dwarves)
all neighbors
if possible, any other fun but non-CPU intensive features
if anyone can rig this up, I will happily name my first-born child after you.
Gen a large world, and as said set all variances to 1600.
Now, if you don't mind aquiffers, lower the maximum drainage (less deserts, more forests) and lower the maximum savagry (by a good 50 or so)
Now, getting the other fun stuff might be a little harder if you need at least one region tile of forest.
Set the minimum elevation to 80 and the maximum to 300 (you will still get HFS producing mountains this way).
Set minimum ocean requirement to 0 and set maxmimum subregions to max.
After this, set all minium region types to 0 (none).
If you want a brook/river set river count to 800 for both pre and post erosion.
After this its a matter of generating worlds and searching for a site that has these options. If you're extremely diligent, you should be able to find a magma source, underground water source, pit/chasm and HFS in the one 3x3 site, although as mentioned this might take a n awfull lot of genning just ot get lucky.
Also, do not raise the minimum volcanoism, it will inhibit your chances of finding flux and layers containing iron ore and fuel.
P.S. To make world generation easy, have world gen stop 2 or 3 years in. Copy down the seed data, and explore the world. If the world has what you need regen the world using that seed data and let it run for as many years as you like. then of course make a backup save so that you don't get another corruption.