There's not really a good way to get started. Basically my advice would be pick one thing you want to change, then scour the forum for any relevant information. Make sure to set the search function to 3 years. It's convoluted but most of the information is out there.
Most of the things you've described are not done in the editor however, they are done through .txt files. This is the most comprehensive guide to using the .txt files, and it really only deals with character stats.
http://larian.com/forums/ubbthreads.php?ubb=showflat&Number=582571#Post582571One thing you could try do it is download Baardvark's Scales mod, which makes quite a lot of changes to the things you mentioned:
http://www.nexusmods.com/divinityoriginalsin/mods/68/?Then see what files are edited and simply work backwards.
