The thing is, it sounds like it's all about you and your dreams here. I don't mean that to sound harsh, you don't actually come across as selfish or anything, but you do sound quite blinkered, and as if you are only seeing the amazing positives and the potential, and not the negatives and the massive impact this will have on the rest of your family.
There's a lot that he's not wrong about as well, and certainly not wrong in raising as concerns. I do agree that for most people, if you have kids early on in life, that means that career development comes later on. It is actually very hard to do everything and have everything all at the same time. I don't mean it's not possible to do both, but it's really hard to do both well, and most of us have to prioritise things at certain times in our lives, rather than having it all.
It just feels like you are approaching it as a fait accompli - I want to do this course to get this job, and you should support me. I can't imagine having that conversation with my DH. I can imagine sitting together discussing what I should do with my career/how to make sure that I was earning a suitable amount to be able to live the life we want for our family, and how to also have personal fulfilment into the bargain. More to the point, I can imagine having that conversation, only in the context of what he also wanted to do career wise, so that as a partnership, we were planning for the future together.
The personal fulfilment is important, no doubt about it, but when we have responsibilities, we need to deal with the actual needs first, before the wants. And your alternative of not doing this and 'get a job somewhere I will hate every day' sounds a bit of a silly reaction. It isn't a case of do this one course now, or have a miserable life, there are hundreds of alternatives between these two extremes.
That being said, it is good to have a dream and some focus/direction about what you want to do, I just think that you need to discuss it with DH some more, and in a more balanced way.
D