I'm using CS as mozilla plugin & i'm found that the simplest way to make loading in separate thread is to run whole CS in that thread. No errors, no problems - at least on Win32 platform.

If "yourmap.zip" resides in "CS/data" directory the command to run your map is "walktest data/yourmap.zip" (assumed "CS" is current directory)

walktest data/box.zip

to Roberto
Delete MeshObject, not MeshFactory. Then you can create new object from the factory.

Somehing like this:

//to remove box
iMeshWrapper* box = engine->FindMeshObject("name of box in map file");
if (box) engine->RemoveObject(box);

//to turn off/on light
iLight* light = engine->FindLight ("name of light in map file", false);
float initial_cutoff = light -> GetCutoffDistance();

//turn off
if (light) light->SetCutoffDistance(0.0f);

//turn on
if (light) light->SetCutoffDistance(initial_cutoff);

For more info you can see API documentation of iEngine, iLight interfaces
http://crystalspace3d.org/docs/online/api/classes.php

https://sourceforge.net/tracker/index.php?func=detail&aid=1311220&group_id=649&atid=100649

in principle 'make install'+'make distclean' is not required. You can set directories inside your IDE to point to CS/include for includes & CS/out/msysx86/optimize/libs for libraries. This is more convenient when updating from CVS because 'make all' will compile the changes only instead of whole SDK again.

Dev C++ is not a compiler, it is IDE. Actually it uses MinGW/GCC for building. After compiling CS plugins (*.dll) & libraries (*.a) with MinGW there are no problems to use them in DevC++ or Codeblocks (another free IDE) to build your own CS application. The same is true for MSVC, then both CS SDK & your application mus be compiled with MSVC.

The HowTo build docs:
MSVC: http://crystalspace3d.org/docs/online/manual/cs_2.4.3.php#2.4.3
MinGW: http://crystalspace3d.org/docs/online/manual/cs_2.4.4.php#2.4.4

I agree. But first time user tries features/demos, making light changes. If the project attracts him there no problem to take sources & try to compile, but at this moment he already know he can obtain from CS. In other words the possible difficulties of compilation don't affect user's wish to start with CS.

Is a problem to have precompiled plugins?
MinGW:
All precompiled/stripped/zipped plugins take 13.5 Mb + zipped libraries 2.5 Mb + zipped headers 1.5 Mb + cs-win32libs 7 Mb. Total 26 Mb.
It's enough to work with CS in codeblocks for example (without debugging inside CS, but who needs this)

Well this is technically very hard as we would have to make a version for every kind of compiler

btw 1, OGRE made this for MSVC. Obviously there are no problems to make this for MinGW (devc++, codeblocks)
btw 2, codeblocks (http://www.codeblocks.org/) has template of OGRE application.

I think it makes a sence to give novice CS users precompiled pseudo-stable version of CS SDK. Look at support forum: "...problem with compiling...", "...problem with building...", etc. When documentation is Ok there is no need to have sources for most people.

You will find good artists for "beautiful level" much quicker if the task of conversion to CS is fully placed on developers. Don't induce artists to make their work in Blender. Blender is great project but habit is big power and it's absolutely useless to fight with fact that most of 3D artists like Maya, 3DSMax, ... and not Blender.

When I've took a look on protomesh sample a wish of writing new mesh vanished

It is not problem to make particles independent. Most of them (emitter, fire, snow, explosion, spiral) use Sprite2D as particle object which can be extended to support independence.
The big problem is to get effect what we want. A particle at the moment of creation must get its start speed from base object + emitting speed. But at the moment we cannot know from base object its speed. At least there no good API-way to make this. Of course we can compare previous pos & current pos and divide delta by elapsed time, but that's very rough approach.

Add alpha channel to the image with alpha=0 in black areas & save as png/tga. Some Photoshop work, not Blender