You won't be able to suspend the process when you're executing sequential steps of service tasks. The reason for this is that they all run in the same transaction.
However, you could introduce 'async steps' for your service tasks. In that case, the transaction will be committed, and the suspend should be honored.
However, I do think somebody filed an issue that suspending the process doesn't yet work fully when dealing with async steps, so it's possible we need to fix that asap.