Here's my scenario: I've just had a job offer from a small startup. I've been in various discussions with them, been through a sort of technical interview and talked at length with the founder.

I've never worked at, or had a job offer from, a startup so I'm not sure on best practice. The salary offered was about what i expected and it also included a percentage of equity in the company, to be vested over time. This all sounds great as I've always wanted to work at a startup, but I have a few concerns that I'm hoping you guys might assist with, and perhaps help with my deliberation.

The startup itself is based quite a distance from where I'm currently located, and would require me to relocate. I'm not averse to this but it just means I want to be extra cautious before I make any decision.

So my questions are:

What is a reasonable percentage to be offered in terms of equity? I would be employee number 4 or 5. Is it advisable to speak to a lawyer about these things? Is there anything to be careful/mindful of?

Finally, whilst there's bound to be an element of risk with a startup, what due diligence should I undertake to ensure any decision I make is right one? Is it reasonable to ask to see their earnings, for example (please don't shout me down if I'm way off base here!)? How might I roughly gauge their likelihood to be successful?

Thanks in advance.