Questions to ask a startup before taking their offer (new grad)?

Assuming it's a smaller startup, and not in the scale-up stage, I'd be wondering why the company is hiring grads and not senior engineers. There are plenty of reasons, but I've seen a lot of startups try and capitalise on "cheaper" grads over seniors. I'm sure it works out sometimes, but it often screams that they're looking for cheaper shortcuts in engineering which is a red flag for me.

I'd want to know what their mix of senior to grad/junior engineers is, if it's strong then maybe they're just starting to scale up a bit. If you're going to be in the first 5 engineers though that feels like an odd decision to me and I'd want to know why. Really, what I'd be looking for is an answer to "why would they hire and spend time on-boarding someone that isn't a senior when they will be under so much pressure to deliver correctly?"

Assuming that can be answered well, I would start to think about what learning environment best supports you. Are you okay being throw in at the deep-end and expected to deliver under pressure? Or, would you prefer a slower paced environment with more time and money to pour into your learning? It works for some people, but not for everyone and you don't want to risk your opportunity to learn in your first 2-3 years in the industry, it's critical.

Before even asking them any questions I would prefer to research the founders, board members, investors and their previous experience. My personal preference is to look for founders that are well connected and have launched successful companies then handed them off for others to run after some time. I try to avoid startups that have leadership with multiple prior criminal indictments.

Whatever is important to you, probably not all that different than any other job. Depends a bit in what role as well but you can expect less guidance which may make it more difficult if you are a new grad.

The one question I'd ask is what your day-to-day will look like, the answer is probably "a bit of everything, young startup, you will grow with the company, blahblah" but at the end of the day there is something you'll have to do and perhaps in startups more so than in other companies that might be things like customize this powerpoint of our pitch for each prospect which may get rather boring.

Is there “on call”? How frequently do incidents occur? Been there done that, not interested.