To afford a home with a purchase price of $400,000, you need to earn $150,000 - 200,000 per year. No LPN or RN makes 6-figure salary. You can afford a home that is 2 to 2.5 times annual income. With a $200,000 down payment on a $400,000 house, you still cannot afford a $200,000 mortgage. Maybe if you held an MSN, and a high level position in a nursing specialty or administration, you might make it.
As a rough rule of thumb, figure housing costs will run you 1% of purchase price per month. A $400,000 house will end up costing roughly $4000 for mortgage, taxes, homeowners insurance. Then add utilities and maintenance. Of course, this is a rough -off-the-cuff - estimate for quickie calculations, and obviously underestimates costs if you don't put enough down, or live in a high-tax area, etc. But quickie estimates from "rules of thumb" have their uses. Even this quick look indicates you are wildly off the mark in your housing dreams. As an LPN, & even after you become an RN, you will be looking for a house about half your current wishes. And DO NOT put all the proceeds from the old house's sale into a new house - save & invest a portion!