“左右” is a noun used after a quantifier to indicate “a quantity slightly bigger or smaller than the amount indicated by the quantifier”.
It is enough to walk at a speed of about 100 to 120 steps per minute for thirty minutes every day.
“加起来” means “add up to”. “起来” is a directional verb used after a verb to indicate the actions which has produced a result.
You can take three to five minutes’ break every day, and that will add up to 5,000 steps altogether.