I was hired to build a website; I thought / was told it would serve as a "calling card" in order to attract more funding and then the situation would get re-evaluated from there. Due to my, I must admit, personal failings, I let the boundaries between client/contractor slip, and somehow I turned into employee #1 (but still a 'contractor') and the --only-- employee. I then ended up building mostly by myself a small B2B business for these assholes while they lied constantly about cash flow problems to me and the sales guys. Long story short, because I wasn't legally a founder, though in all other senses I was, when I got shoved out the airlock, there was no legal recourse I could take to get back at these people. They even tried every tactic possible to delay paying my and the other people's invoices at late as possible and as little as possible when we all quit in the space of two months.

So for question 1. It's about power. The relationship between you and "the company" is different if you are an employee versus a founder. As an employee, you aren't legally deserving of access to financial information, like cash flow. Or board meetings. At the end of the day, all that really matters is the legal paperwork and that will be different if you are a founder and not an employee (stock for employees, or options, are always mostly worthless). And as a founder, you get access to any profit, but you wouldn't as an employee. And as a founder, you would have far more of a say in how the company is run than you ever would as even employee #1

So if you are --sure-- you have a good relationship with these other people, and that they are not professional sociopaths like those I dealt with, then I'd say you could have a case to be considered as an founder. You say you are helping them with research etc - to what extent, how much, etc?

OTOH, how much responsibility do you want to have, in legal terms, and otherwise? Being a founder would require more - more complex taxes, etc, and more of a concern over how the company is run and where it is going. What do you think your role in the organization might be? I was effectively the CTO, but because I "wasn't", I didn't really have the power that comes with the title. And I was so caught up in doing the actual work, and I didn't complain enough about the overwork, that I left all these non-tangible non-technical considerations slide - and at the end of the day, if you are intimately connected to the founding of a company, these intangibles are a lot more important than anything else, including money.

To be paranoid, what if you sign on as an employee, and things go south? Can you walk away without any attachment to this company you've helped build? To what extent are you willing to play dirty hardball if the relationship goes bad? It'd be easier if you have the legal status that being a founder offers. Run all contracts past a lawyer and play "what if" scenarios to make sure you are not caught flatfooted.

I took the hard road; it was all a severe crash course in how business actually is done, versus the blather about 'company values' and 'ethics' and that nonsense. Some people are nothing but more than scoundrels and so make sure you are sure you have evaluated the character of these people thoroughly before getting into a relationship with them. I wish you luck and hope you don't go down the road I did.