My initial DB schema was pretty bad. We did at 2 schema rewrites and migrations from the launch to 5M users. Each time it took 2 weeks of sleep less nights.
The machines today are really powerful. You can do a lot with 244 GB RAM machines backed by SSD.
Someone who doesn't have the skill set to be able to scale once they get traction - it's likely they will not have the skills to design for scale at start.
My recommendation to everyone would be pick a language and db you are most comfortable with and get started as soon as you can. You will fail on the product side a lot more times before you will fail on the technical side.
And if you are failing on technical side, reach out to me. I will definitely be able to help you find a way out. I am not sure if there is any product guy in the world who an make a similar claim on the product front. However there are at least dozens of technical guys in the world who can make a claim like I did.
So focus on launching the product as soon as possible. Work hard, reach out for help if needed. You will eventually get success.