Looks really nice knorke. :)
And small enough to be distributed within default package too.
So, if you do not mind, I will include those as the default prefab tilepack together with SME.
I can see it would be very nice to have some kind of rendered preview, when using prefabs at a scale this small. (Still prefabs have the nice feature of just trying it out. If it was wrong, just paste it over again.)
@1: Currently it is just windows' current directory. But you are right, makes sense

@2: Instead if this I will try to create some kind of prefab-preview rendered on top of the cursor.
@3: Easy enough.
@4: Showing coordinates aligned with prefab: easy. Overlay could be possible the same way as other overlays. Needs experimenting.
@5: How to show/select this? (I included the commander unit as a feature to get an idea...)
@6: Easy enough.
@TexGen:
There are only 2 textures supported for steepness now. (Flat and Steep, for each heightlevel.)
Example:
Flat1=0.005;
Steep1=0.03;
Until steepness reaches 0.005, only Flat texture is used.
Between 0.005 and 0.03 Flat and Steep are blended inbetween.
After 0.03 only Steep is used.
So if you want to always blend between both textures, Flat1 should be very small, and Steep1 very high. (Exact values need to be tested.)
@Smoothing map: I think there is a hotkey "S" for smoothing out the whole map.
It uses the brush-strength of smooth brush. (heightmode smooth).
The brushstrength determines which is the maximum height difference which gets smoothed. If you plainly want to smooth everything, just move the strength to 1000, and in 3D window press S. (lower values are for preserving steep cliffs)
Another idea would be to smooth the prefabs beforehand, so you do not need this smooth-step at all
Hope it helps :)
Frostregen
PS: It seems the prefabs do to fit exactly together on different heightlevels (sceenshot from your map, at floor of ramp to the right.)
Is this an artifact from using filters afterwards? Or could the prefabs use some improvement? (LevelOverlap setting?)
Also the ramps themselve look dithered. Maybe use 16bit heightmaps instead of 8bit? (I will investigate this further)