Am I better off than I think?

I'm wanting to understand my fiancee and I's coast fire number, while also considering a few life circumstances that may come up over the next decade. We are both 30, and I work a very high stress job in construction that I'd like to see when it's possible to leave and do something part time I'll enjoy more. I also need to consider kids, which could be a possibility in the next 3-5 years, in which case I'd really like to be a stay at home mom/work part time. Obviously that would only be possible if we're in a financial position to do so. Here's some of our stats:

• Total 401k, Roth IRA: $600,000

• Monthly savings: $4k

• Savings for house down payment: $130,000

• Current monthly expenses: ~$4k

• Retirement monthly expenses: assuming ~$8k in today's dollars

• No student loans

• 2 Paid off cars

Some coast fire calculators say we'd be able to hit it by 55, even if I went down to part time work tomorrow. Others say we still have quite a bit left to invest.