dynamesh should always fix that weird geo you have after you pull the arms out. It won’t smooth out the geo, but it should create evenly spaced geo that you can smooth and continue to work with. Turn on your Polyframe to check. If it isn’t updating then you’re doing something else wrong with dynamesh and you might want to ask about that.
As for your arms being broken in your last image, that was you using a brush that was too large and you sculpted through the mesh and pull the backfaces as well as the front. You can avoid this a couple of ways. First make sure you’re always moving around your geometry so you’ll notice that issue soon enough and you can just undo to bring it back. Second, turn on backface masking in your brush>automasking (this is a per brush setting). To fix, you’ll have to resculpt that area. I would simply insert a cylinder and dynamesh it all so you have a volume to work with again and correct the sculpt from there.