Calling all military wives for advice please!

So my fiancé is going into the Coast Guard in May. I'm super excited for him it has been something he really wants to do. The problem I'm having now is that he thinks it's a good idea to get married before he leaves. But my MIL is completely opposed to it saying that we should wait and let him do his own thing. I know that the military is a huge adjustment so I don't know. I want to support him but I'm afraid of angering my MIL.  
Another thing is I live with him and when he leaves I won't be able to afford our place alone so I'm moving in with my parents while he is gone. I'm not familiar with housing arrangements in the military. Is it better to just wait or to get married first? 
Any advice is welcome. Thanks so much.