Husband is wanting to start a buisness 6 months before I have a baby?

Here is the back story. As of right now my husband and I both work. We have a 5 year old son (he is mine from a previous relationship). We got married last October. We bought a house last year. So we have lots of bills that came along with that. As I right now we are barely making it. I am due with our child in November. We both know that we will not beable to afford daycare for our infant. So we decided I would stay home after I have the baby. Thing is, my husband has got the bright idea (he gets these OFTEN) to start up a pool cleaning buisness. He has no prior experience doing this. My uncle does this as a side job and for the past 3 weeks has been showing my husband how to do it, only ONCE a week. He hopes to take off on his own soon. He knows my feelings already but he just keeps saying this is going to work out great. He is going to make enough money to completely support our future family of 4. I am terrified. I want him to focus on finding a job that makes more than his $300.00/week he is bringing home right now. I don't believe that starting a buisness 6 months before having a baby is a good idea. Especially when we are barely making it as it is. He still has his job right now. He is wanting to start making enough with this pool thing to quit. I just don't know what to do anymore. He is a dreamer and I am a realist. I'm freaking out as the months get closer and closer to November. If someone could give me advice if they have been thru this. Either from my point of view or maybe you were like my husband. I just need to figure this out. Thanks in advance!!