You can get a brief description of the modes if you hover over the mode name in BFE.
Also, in the game folder there is a folder named BOOTLEG_ORIGINAL_READMES that contains many of the mod documents.
You cannot mix and match save games. Save games created in Hardcore mode will not work in other modes.
In Bootleg 0038, there is a bug that prevents Hardcore mode from working correctly when Menu Overhaul with ReTranslation is installed.