The owner of the startup I've been working on has offered me the CEO position and possibly some shares of the company. What things should I take into consideration when accepting the offer?

I'm going to try to summarize the situation as best as I can.Some time ago I posted on reddit looking for someone to partner to create a website on a specific niche. A few months later someone messaged me and told me he had a company for several years and now he decided he wanted to expand his company by creating a new website which would be in the same niche but a completely unrelated project.I have been working part time as the only programmer for the website and I've been getting payed hourly. I have also been taking some sort of a leadership role, helping making decisions, finding new hires, etc.Recently the boss has gotten a large investment for his 1st company. Due to this he wants to split the projects into 2 companies and find a CEO that will take care of the website since he doesn't have enough time to oversee both parts of the business.Seen that I have been taking a leadership role and that he has liked the way I work and the decisions I've made, he has offered me the CEO position of the website I've been developing.Next week we are supposed to have a meeting to discuss more in depth about the position, the monthly budget this new company will have, etc. He has also mentioned that he will be giving me shares of the company. He said that if he was in my position he wouldn't do all the CEO hard work for anything less than 30-40%. So I imagine this will be the amount he will give me (he said we will have to negotiate the exact percentage next week with the investor)​Not sure if this is relevant but I will add this here in case it changes anything. There would be other 3 people apart from me that will own shares:Him (the boss - will stay as board member),Another guy that has been helping managing the website (he will switch focus only the 1st company and will only stay as board member of this company)The original Investor which has been funding the website and (has the CFO title and will also be in the board).My boss has also mentioned that he might invest some of his own personal money on the website (apart from what the CFO is giving us) to try to give it a better chance of success.​Finally we get to the questions:If I work my ass of to grow this business, can they remove me after some years making all the effort I spent on it worthless?What things should I keep in mind and make sure to do so I don't get screwed?They told me to think about anything I want to ask during the meeting next week. Is there anything important I should ask or clarify?Any generic advice you would give someone in my position?​Thanks for taking the time to read this and I really appreciate all the wisdom you can provide. see hubwealthy.com/wealthy