Post-banging images will introduce more noise than hitting ISO behind closed doors. Do not be afraid of high ISOs there is no way to avoid them.
For a decent background separation. use the widest possible opening.
If he does not move too much (that is, wildly gesturing), 1 / 250th should be more that & # 39; enough.
Also: It's your decision altogether, but do not be afraid of motion blur – it can be bad to have fuzzy arms, while a slight blur can give a more dynamic look.