-I have read a bit about Aces but I don´t see any advantages with that because I just have one type of files!
Don't bother with ACES unless you require it. Most LUT's and many of the color correction tools in Resolve do not work properly in ACES.
-What colorspace to use in the camera raw tab? BMD or 709?
Use the BMD to get the DR you want.
-What node structure is the best? correction before or after look/lut? when to use scopes? when to correct skintones?
I typically do base lift/gain adjustment -> Individual section of the scene adjustments -> clean up skin -> stabilization/noise reduction -> Then apply look
