When should I setup business accounts for my product?

TL;DR probably fine to use personal accounts, business accounts have benefits but also considerable monetary and time costs which may not be justifiable given a project's traction.

I feel like most creators will launch under personal accounts and keep things as a personal project (sole proprietorship) until there is some need or traction that justifies forming an actual business (corporation). I think this is usually sensible to avoid over-investing in something that might not work, unless someone is doing something that already has traction (like a bunch of funding or customers on the waitlist) or there is a clear upfront need/requirement for a company (perhaps for regulatory/licensing reasons, etc).

Ignoring anything money/revenue/payments related for a second, I can't think of any significant risks of using personal accounts for personal projects that have not reached your personal threshold for turning the project into its own business entity. "Personal accounts" meaning your personal Gmail account, personal Notion account, personal Amazon account, etc.

Just to brainstorm, maybe business use on a personal account could breach a service's terms of service for using a personal service for business purposes, although if the personal project is not an actual company yet, that's probably not a risk (and it's unlikely most providers will have this limitation for non-incorporated entities). Even if it was, I think it's nearly impossible for providers to enforce how their services are used. It's also possible business accounts have a specific feature or need that would be helpful for the business, like needing a Google Workspace account to have emails on a custom domain like support@golanding.page, but this should be apparent to you when you are choosing the service.

Going back to money/revenue/payments, after there are actual paying customers, there are tax implications of not having an entity. Taxes may be higher for using yourself as the business entity rather than a company. The reason many people incorporate is to separate business risks from affecting yourself, for example if someone were to sue the business, or if you were to default on a business loan. People probably have different estimates of the likelihood of risk (IMO low but not zero), and it depends on exactly what the project is doing. This article talks a bit about the tax and legal risk effects of incorporating: https://smallbusiness.chron.com/difference-between-proprietorship-incorporation-55604.html.

Might depend where in the world you are really as to local tax laws etc.

Places like stripe and paddle might be able to be set up now without having a business account, if you make any money just hold it there for a while. If it looks like starting to gain traction then set up a business account to get the payouts into.