You are investing a couple years of your life in this. That's probably investing a couple hundred thousand dollars of opportunity cost vs a job at large tech company.
You have plenty invested. You'll do well if they do well. Spend your liquid investments in something diversified.
- sincerely, a moderately lucky person who has joined 3 companies before employee 15
There are major benefits beyond tax savings. If you quit before a liquidity event you can easily keep the vested equity without worrying about paying taxes on unrealized gain.
If you wait, you get substantially more information. A company that makes it to a Series A has a much higher chance of succeeding, and you'll typically know that in your typical tenure of 1-3 years as a junior dev.
If you want to spend $10k cash on buying startup equity, at least call yourself an angel investor and go find a company that's willing to issue you a note that converts to preferred stock. It's too easy for a company to have a couple of missteps and wipe out most of the common stock value, even much later.
If you can't afford dropping $10k to buy your equity then you can't afford taking a $10k lower base salary -- let alone a $100k lower base.