As you are demonstrably worse off after your time as a sahm, you have a very clear case that you were disadvantaged to your DH benefit and therefore should push for a bigger slice of assets 60% plus.
The real problem is how much the courts will accept as DH income/company value.
Can you get together any paperwork about the businesses income? If it's just DH with a company value of 450k then it must be making a considerable sum. Beware that ex might start drawing minimum income (if he isn't already) in order to minimise maintenance and how much of the shared assets you get
As a shared holder you should be able to demand a general meeting where income/profits must be shown. I believe you are legally privy to this as a shareholder, he can't hide this from you.
I don't know how to protect yourself in the case if him simply shutting down the business and starting afresh. I would certainly attempt a clean break rather then asking for portions of profit as a shareholder for this reason.
One question to ask now. Are you recieving your share of dividends? If you are currently separated, is withholding your income from the company?
Is it the kind of company that can just change names and carry on?
It might be a good idea to speak to a business lawyer about your rights here.
Do you know what his income is? If he is a very high earner compared to you, you may be due spousal maintenance but I understand this is hard to get, would be for a period of time following devorce and a decent clean break would like be preferable if you can get enough to survive on.
Will you be primary carer for the children or will it be 50/50. If he is a high earner then 50/50 doesn't necessary mean no maintenance is due. Him being self employed can cause issues with this so if possible I would try to tie down a maintenance amount in court if you end up there. Again this is why the business finances will be very useful to have.