What is your target income need for FIRE? How do you plan to allocate the remaining @$900K into rental properties, what will those mortgages be, and how much rent do you anticipate those will throw off? Can't really say without the context.
Generally, a house you plan to live in should be viewed more as a consumption good than an investment, because it will not return you any money until you sell. So plug the cost of that mortgage (plus associated maintenance and utilities) into your post-FIRE budget; then estimate how much income you can throw off with your remaining $900K invested in leveraged properties. That will give you the gap that you will need to cover over the next few years with additional savings/properties, which in turn will allow you to evaluate whether you are on track.
But FWIW, $400K sounds high for that part of the country. And if you were relying on traditional investments and the 4% rule, it would be way high -- your post-purchase 'stache of around $900K would throw off about $36K/yr, which would basically be eaten up entirely by mortgage and utilities.
