In my opinion your number is $900,000 which is:

1500 / month * 12 months / year * 2 for taxes (this feels genetically safe as a high bar but maybe not) * 25 in order to safely pull 4% yearly forever

Trying to come up with a plan to get a business running that can safely yield 1500 / month (more for taxes) can be dicey and prone to all sorts of risk, and the time horizon is unknown. Just saying, don’t discount leveling up with learning and trying to move upwards, keeping your current lifestyle, and saving your way up.