A few question on starting with a flashforge creator pro

Hi everyone,

I just got a new flashforge creator pro for which I have a few questions

I'm using PLA, I tried different temps for bed and extruder that seem to work better
I first leveled the heatbed for a 0.3mm precision printing which worked really well, no warp on corners and the pla had a good adhesion on the bed.
Then I went to 0.15mm precision and the PLA would not stick to the heatbed, so I figured the heatbed wasn't really well leveled and lowered it a bit. Now it prints but has a tendency to warp on corners after I'd say 15 to 20 layers. Also this printer is a dual extruder, and it seems that when printing big parts, the second extruder scratches the surface of the part printed by the first one (I can see it bumping into it and going over the layer scratching it). Is this normal ?
Will I have to re level the bed every time I change precision?
what seems to work right now is 215°C for the extruder and 55 for the bed

Thanks for your help

Antoine