Trying to decide between Google, CZI, a series B startup and a new venture

Hi, I am super happy to have so many options at this point, but now, I need advice. I have Front End SWE offers from CZI (chanzuckerberg.com), a series B startup and a very young startup. About Me: - 10+ YoE. Startup experience > 6 years. Ex-Yahoo, Ex-Infosys. - Long term goal: Start my own company. So, need a big brand name for VC funding in future. Also, need relevant experience and confidence to start my own venture. - Enjoy working on products end to end (from market research to design, development, deployment, marketing, etc everything). - Looking for opportunity to work on a large large user base systems. Worked for <10K users. - Want to give back to society. #Google: Pros: Big name. Dream company. Amazing talent to learn from. Maybe opportunity to work on Area 120. Will develop for millions (if not billions) of users. Cons: I guess I will be asked to work on a very specific problem and solve it for huge user base (like designing a sign in system or emoticons on messenger, etc). Can't switch teams for 1 year after joining. #CZI: Pros: Reasonable name. Great talent to work with. Will be working on a more ambiguous and bigger scope of the problem (in comparison to Google). I know my hiring manager and would absolutely love to work under her. Making a lot of efforts for social good. Will develop for hundreds of thousands (if not millions) of users. Cons: Heard about the politics at higher management. Not sure if "doing social good" is a mask from founders or a genuine attempt. I know that employees are pretty committed. No stocks - but I can invest on my own the base salary difference. Series B #startup: Pros: Doing social good - genuinely. Getting higher title and responsibilities Hope that one day it may go big - I think at least 4-5 years. Cons: Very junior team + junior manager. Not sure who will I be learning from - I don't want to be the smartest/most knowledgable in a room. TC is way less than bigger companies. In best case will have thousands of users. Very small company (<10 people): Pros: Can get any title I want Very high risk, very high reward Will get to build a company from scratch with relatively lesser risk - great learning for my long term goal. 0 users currently. Cons: Not a co-founder. Maybe a founding engineer. Super low salary. Not enough trust in founders or if the company will go big at all. In best case will have thousands of users. 0 users currently. What would be your advice? And please add a comment on why? UPDATE: Thanks all for the advice and votes. I, being on H1B can't start a company immediately. But, I did join CZI - stayed there for about 6 months and could not make the opportunity work. Now, I am joining Google. Thanks blind and @dontbe3vil for telling me that Google's offers are valid for 1 year. About starting the business, I am trying that as a side hustle as many suggested. I learnt that best is to build a product, and start selling/distributing it - company will form on its own, in it's own time.