how deep are you trying to cut with what size endmill? I usually program for the radius of what I am using for each pass. for a .25 endmill I set each pass for .125 with my finishing passes for .1 or a bit less.
The problems you list also point to many different things all over the map. I might suggest doing a shallow cut of a circle and square. I started wtih 20, 40, 60, and 80 mm with a 1mm depth.
this allowed me to see how accurate it is in order to make adjustments.
I’d suggest start with something simple and consistent and post your results so the community could help with diagnosing your issue.
I kept a log here of my test and results. it may help. There are many others i looked at to reference their process of tuning.