Two thoughts. First, as others have mentioned you need to look at medical. The good news is that you will almost certainly be eligible for ACA subsidies, which helps at least until the ACA does get repealed. (Heck at < $20k year you might be eligible for medicaid.)
Taxes were also mentioned, however you will likely owe very little in federal taxes, since you'll get at least a $12k standard deduction. And depending on how your $600k is structured you may have already paid taxes on it.
But some additional things to think about:
- major home maintenance costs. Maybe you haven't had to spend money on the house in the last year or two when you've been tracking expenses, but at some point in the next 10-20 years you may very well need to drop $10k+ on a roof, or $3k on a furnace, or $500-1000 on appliances, etc. You should consider what expenses you're likely to have and amortize them over time.
- similar story with cars. maybe you paid cash for a honda accord 5 years ago so you have very little expense since then, but down the road you may, and you may need to replace the car. (If you're really only spending $20k, though, maybe you don't have a car at all.)