It's worth noting that what Bernie Sanders is saying he will do is more akin to ideal circumstances than realistic goals. Politicians in every country generally have a door understanding of limitations (both economic, political, social and constitutional) that restrict their ideal policy implementation. The U.S system is built on checks on power and so its very difficult for any President (no matter how moderate) to accomplish their policy goals regardless for controversy.
I'd say Bernie is making big claims due to his wish to change the course of Left-Wing politics in the U.S. Realistically he can only accomplish a moderate amount of reform, but selling it on a socialist basis will allow for him to push forward these ideas with greater ease as he'll at the very least have a mandate with which to tackle these issues, if not the economic or political ability.
It's kinda like how Donald Trump said he was going to tear up NAFTA until he realized (upon entering Washington) that NAFTA plays a vital role in the U.S's trading power with Canada. Or how he thought Mexico was going to pay for the border wall due to a trade deficit (which makes zero sense for a multitude of reasons.
As for the comments with regards to the U.S military: the U.S needs to maintain its military no matter what, the U.S holds a hegemony and without the means to back it up would open up the world to another rising power (China) to start exerting hostile influences on other nations.