The key file editor is something you’ll have to figure out on your own, for the most part. It’s not something that can be quickly explained. There are instructions provided, however. Both the editor and the instructions should be in the /docs folder in your BMS directory.
If you really don’t want to figure out the key file editor, you may try the “BMS Alternative Launcher”. It will be easier to use, but it’s a bit glitchy still.
The easiest way to set up the mouse stick is to use SST. Set the mouse stick X/Y axes to “bands”, then bind the push AND RELEASE for the appropriate slew key presses. If you don’t bind the release, you will have problems.
About your profile illustration, you need to have the TMS hat included somewhere.