If you haven’t publicly launched yet, then it’s hard to work backwards from what the customers actually want. What you may have to do is try to theorize who your main customers would be and what they would want, and then work backwards from there.
In such a case, I would encourage you to set the SLAs relatively lower, at least until you can gain some real knowledge from actual customers.
You might also want to approach some prospective customers and bring them into a private preview version (protected by NDAs), so that you can start gathering that data earlier.
Also, ship early. Ship an MVP earlier than you thought possible. It’s okay if it’s all held together with spit and bailing wire, at least you’ll be able to start gathering data sooner, so that you can start the real business of actually building what the customers truly want.