It's the same engine roughly, but there will definitely be large differences. It's hard to say how much will change. The scripting language, both the story scripting and character scripting, seem to be largely the same. Dialog trees use a new tool, so don't bother with that. Terrain design will probably be fairly similar, hopefully with lots of quality of life improvements though.
I'd probably just wait to Sep 14th. Assuming the new editor will be released with good documentation, it should be a smoother learning process, and you won't necessarily gain a ton of experience with the old editor in a month anyway.
I might suggest taking a look at the Epic Encounters Develop edition, and seeing how the file structures work, the character scripting (Sandpie put lots of useful comments in), stat files, etc. You can also see what I did in my bard mod to get an idea of where those kind of stats are stored. I'll release a tutorial fairly soon after release unless Larian posts a very thorough tutorial themselves.
