How many story arcs in a campaign? And advice needed for interesting pc arcs

So basically I'm trying to improve my games. Ive noticed that Im not very good at making like "story arcs" idk if you call them that. They kinda bleed into each other and idk if thats normal. Im also not sure what would be a realistic amount of arcs? Weve almost kinda finished our first one ig? With the end of the arc being defeating a small camp and acquiring an artifact. Cause from what I gather you want to have like "goals" that your party works towards? So is it normal for them reaching a goal being the end of that arc? Im also not sure how many arcs is realistic to have in a campaign? Like would it be okay to have like shorter ones after this? Like would 5-6 story arcs be too much?

Is it realistic to have down time after receiving that? Cause they havent had much downtime. Weve played like 8 ish sessions and in game that would be like two weeks at best.

Im also struggling with where and how do I fit in interesting pc arcs cause my friends gave me a lot to work with. But im still kinda figuring out how to do those type of arcs since weve only played some premade adventures that were like 3 levels long so we decided not to include them. Like do you have them be side quests do you weave them into the story itself? Are there any tips you guys have for this?

Sorry for the amount of questions im just really looking to improve any help is greatly appreciated :)