Hey, @RomainPC-0-1-1-1-1-1-1
Let's see if I can answer everything.
It's actually possible to store the application outside of the sdk repository.
Here is a link on how to do that:
https://developer.sony.com/develop/spresense/docs/sdk_set_up_en.html#_add_to_a_different_directory
The flashed kernel is always inside the sdk folder, yes. And it's called nuttx.spk.
About not seeing the Kconfig in the IDE apps:
We don't need a Kconfig file on the IDE because the whole point of this file is that we can see the configurations associated with our example once we open the configuration menu in the CLI.
In the IDE, this configurations are chosen for you by default in the application.mk file.
If you want to change the default values, you can go to your application Makefile and input the values you want. But if you notice, in the bottom of the Makefile of an application created with vscode, you have an include to .vscode/application.mk.
About compilation time:
I don't think the amount of examples have that big of an impact, since going in and out of directories is pretty fast. What I can recommend to improve compilation time in the VSCode IDE is going to .vscode/build.sh and changing adding -j after the make command.
Before:
cd ${SDK_PATH}/sdk
make
After:
cd ${SDK_PATH}/sdk
make -j