I’m using an ergopouch for my 8 week old with his arms in. Is this safe? Is the 0-3 month size. At what age is it unsafe to have his arms in? (There is an option to open them and have his arms out). He has not yet started to roll.

Some babies do not respond well to wrapping & will not be wrapped or have their arms out from birth.
This applies to babies being wrapped using a muslin wrap or swaddle suit such as you are using.
Red Nose recommends that you modify (have arms out) any wrapping/swaddling from about 3 months in preparation for rolling or before if baby is attempting to roll prior to that.
Discontinue wrapping baby as soon as baby shows signs of attempting to roll.

If babies are wrapped, they should always be placed on their back
Because of the likelihood of rolling onto the tummy, current advice for excessive crying in infants, suggests babies should not start wrapping after the fourth month, to un-swaddle as soon as the child signals they are trying to turn over, and always to stop swaddling before the sixth month, because after this age infants will be able to roll over
Modify the wrap to meet the baby’s developmental changes, e.g. arms free once ‘startle’ reflex begins to disappear which is usually around 3 months; (Moro or ‘startle’ reflex should have disappeared completely by 4-5 months).
https://rednose.org.au/article/wrapping-babies