Is it safe for a newborn to sleep in a sleeping sack with no arms he is strong enough to push himself around and maybe over. Do we need to do anything else?

How old is your baby?
Is he rolling?  - if your baby is rolling he should not be wrapped, he needs arms free.
Are you referring to a swaddle type sack where his arms are closed in bag?

Red Nose has the following information about swaddles/wraps.
https://rednose.org.au/article/is-it-safe-to-wrap-swaddle-my-baby