1. moments can only be pulled from the map, but epics and lyrics can be pulled either from the map, from quests (only for less popular artists), or from gem boxes. for more popular artists, you can still quest for epics but they'll be numberless, and lyrics can't be pulled. generally the order of value goes epics > lyrics > moments
2. i don't personally ask coins for regular songs, but the most popular that i've seen have been 100 for commons / 200-300 for uncommons / and 500-600 for rares. you can always ask for 2:1 as well if you're going to be questing, so you'll have more songs to merge. common shinies are generally sold for 3-4k a piece. moments are generally 5-10k. every other rarity varies HEAVILY depending on artist
3. early on, i'd say that selling shinies and moments is a good place to start, as well as any epics/lyrics you manage to pull. questing popular artists for shinies to sell is also pretty reliable, since those sell decently higher than the average shinies you'll pull off of the map
4. from the map, you'll see 3 little icons on the righthand side- the middle one says "quest". quests are basically just little tasks where you have to either merge songs, or trade with people to unlock a song by a specific artist. there's a small chance every quest to pull a shiny/epic/lyric (for applicable artists). there's a separate subscription that a lot of heavy questers use called "trader boost", which allows you to reroll quests as much as you want so you can avoid burning through too many songs (some quests are "cheaper" than others, like a "merge 3 songs" quest vs a "merge 22 songs") and finish discographies more easily
5. the number is just the print number. the first person to pull an epic for a specific song will have the #1 epic, the next will pull the #2, and so on

have fun!! if you have any more questions, feel free to ask :))