I have somehow managed to make a little gizmo that primarily consists of an MCU, some sensors, and wireless connectivity. I have gone through the process of making the initial prototype, then designed a board and made an SMD version. It's small and it works nicely. It also has a nice case that I managed to 3d print then cover in a little homemade silicon sleeve. I made it for myself for fun but it works really well and everyone seems to want one. I could make maybe a few dozen of them by hand and sell them off to the people I run into that want one, but what if I run out quickly? It seems possible enough that I feel a little panicked at the thought, simply because I don't know where to start.

Where do I even begin to figure out how to take something to market? Is there a standard resource library for this sort of thing? I see no other question on the EE SE that asks quite what I'm asking (most people are looking looking for design or product advice, sigh, but I've already got that done), so maybe this is completely the wrong forum (another hint: I have no idea what to tag this), in which case I'd be happy to move it somewhere more appropriate.

Other pertinent info: I'm in the USA (NYC area) and possibly could be interested in shipping to other markets (Europe, possibly Asian markets) down the line.

Types of questions I am hoping to find advice for:

How do I find manufacturers for the different components (PCB, getting it soldered together, case, etc.)? Or maybe it's better put to say that I'm trying to find out how to shop manufacturers.

Should I split manufacturing to try to prevent IP theft?

Does the shop that assembles the boards also program them?

Certifications???

Marketing and distribution... ??? (I have a decent idea of how to get started here, but resources are always welcome)

Things I'm missing completely?

I feel like I know how to find what I need to engineer something and where to find general business advice, but the chasm between the two seems swampy and mysterious to me.