NIST generally publishes excellent guidelines on operational security for academics, and commercial firms.

As a "solo" anything you are going to fail sooner or later. At minimum one requires a gray-beard IT person/consultant with a vested interest in your survival, legal consultant in corporate contract/employment laws, legal consultant in Intellectual Property (Copyright/Trademarks/Patents), a commercial Accountant familiar with tax laws, and a customs broker to handle international shipping rules.

No one is an "expert" all the time, but without key people a small firm will get squashed pretty quickly. =3

What would consulting a corporate contracting expert do if you have no employees? Not to mention the customs broker... I doubt my local plumber or a freelance software engineer has any of these.

Yes, this is pretty good and you should most definitely read it - https://news.ycombinator.com/item?id=50347164

If you succeed to read it (the admin writing style of NIST is quite dense), it's quite good.

It's a bit procedural and admin focus... but if you execute all of it, at least it's easier to defend yourself during an hack towards your clients or third parties.

I would have prefer something a bit more technical, but it's a good entrypoint, at least to help hire or consult a security professional.