Your domain (yourshop.com) is the permanent address of your business online. Websites get rebuilt, hosts change, marketing companies come and go. The domain is the thing that survives all of it, carrying your Google history, your customers' bookmarks, and every business card you ever handed out.
The domain must be registered in an account you control, paid with your card. Not your web guy's account. Not the marketing agency's. Yours. This is the single most common trap in this industry: a company registers "your" domain under themselves, and when you try to leave, your address is their hostage. The polite ones charge a release fee. The others just keep it.
Usually $10 to $15 a year for a .com at an honest registrar. If you're paying much more, you're paying markup, not value.
.com still carries the most trust and is what people type by default. If your exact name is taken, a small variation with .com usually beats the exact name with an odd ending.
Practically no, if you keep your registrar account secure and your email current. Turn on two-factor and don't ignore renewal emails; those are the only real risks.
Rather have someone who does this every day handle it? That's the $75/mo plan. Or keep going solo, that's the whole point of these guides.
The straight answers Text Nick