Capitalism is an economic system where capital is considered a valid input to the production process, worthy of renumeration. Contrast with some other systems where labor is the only valid input.

Capital is material wealth used productively.

Capitalism empowers ownership of produced good by laborers by funding new ventures where laborers can be more self-directed than if they were forced to labor under the direction of others. Capitalism erodes control from laborers by introducing a non-labor stake in the venture. Both are true.

An artisan who sells what they produce is free to be a capitalist or not, the two are unrelated.

Such a person cannot exist in a society without private property, as "selling" is not a valid concept in such a society. Artisans in general would still exist, though, and probably more abundantly.

An artisan who has more work orders than she can fill alone can expand without the methods you describe. She can form a partnership with another artisan, and teach or otherwise share her methods of production, tools, and branding. This could be an equal partnership or something more like taking an apprentice.

The distinction between worker coöps and other businesses is important, but it's also important to recognize that coöps are a subset of businesses, not an opposing type of entity. Coöps have just as much ability to behave in a predatory manner towards consumers, and almost as much potential to seek self-perpetuation and growth at the expense of their environment. That they will be less predatory towards laborers is nice, but it's not enough to make them "safe".