I'm encountering some issues while retopoing. Still learning it so my retopo mesh probably won't look that good.
First, I tried to start the process with symmetry/virtual mirroring on. It turned out to be really painful since the mirror side were constantly flipping. Adding faces to the left side, then the program says I'm working on the wrong mirror side, changing to the right side, but when I tried to add more faces there, it flipped to the left side again. Rinse and repeat. So I just made the left side almost ready without symmetry and turned it on later and then it worked fine.
Second, how can I stop the program to delete faces from somewhere else than intended place? For example, if I deleted some faces from inside the mouth, I noticed that faces from the ear got deleted too. I have to click a good angle in the viewport so that there is no other faces behind the area I'm working on so that nothing else gets deleted. This is a problem when adding single faces at a time too. It will snap to some other face behind the area. Like in the front view, it would snap to the neck.
Third, the process was fine with smart retopo tool, but when I used R-Fill on some areas, the faces got different colors and they didn't change to the original color when attached to the other mesh. When I applied symmetry, those areas are empty on the other side. Some areas with different color also have red outline, no idea what does that mean. The attached image is showing this problem. I took back to the previous stage with no symmetry applied so I need to figure this out to continue working with this mesh.
Fourth, the R-Fill could work nicely to fill some larger areas, but when previewing it to the area (and applying it), the faces appeared to be inside the high poly mesh, not snapping to the surface of it and following its shapes. The second image is about this.