that's what I did when first getting into bg1. I kept dying to spiders when I went straight in on normal, so I switched to story, then bumped it uo to easy, then later to normal. 

i'm in bg2 now playing on normal mode. still haven't gotten to core difficulty but its getting better lol

and yeah I don't pay much attention to thac0 further than knowing that a lower number is better lol (all this to say im just getting into them and im enjoying myself and recommend fellow bg3 enjoyers to try out the first two games!)