You should be ready to wear multiple hats, even though it's nowhere related to your domain. Depends on the person if this is a pro or a con.
You need to consider all the stigmas that are around startups, like poor wlb, less pay and whatnot as this will be quite common in smaller setups. (not that other companies won't have this problem). Considering these things, make sure you're getting fairly compensated if not more, otherwise it's really not worth it IMO.
If you're genuinely interested at working in this setup, then forget whatever I said.